Optical recording medium, and recording method and recording apparatus for optical recording medium

ABSTRACT

In an optical recording medium having a plurality of recording layers on which information can be recorded by irradiating a laser beam from one side thereof, an optimum recording power to each of the recording layers can be determined. The optical recording medium has a plurality of recording layers on which information can be recorded by irradiating a laser beam from one side thereof, and each of the recording layers has a power calibration area (PCA) for optimizing the intensity of the laser beam.

TECHNICAL FIELD

The present invention relates to an optical recording medium having aplurality of recording layers, on which recording or reading areperformed from one side thereof, and a recording method and a recordingapparatus for the optical recording medium.

BACKGROUND ART

Various types of optical recording media such as CD-R, CD-RW, DVD-R,DVD-RW, DVD-ROM, MO and so forth are widely recognized and spread asexternal storages for information processing apparatuses such ascomputers because they can store a large volume of information and canbe randomly accessed easily. With an increase in quantity of handledinformation, there is a demand to increase the recording density.

Among various optical recording media, optical disks having a recordinglayer containing an organic dye (also referred to as a dye containingrecording layer) such as CD-R, DVD-R, DVD+R and the like areparticularly widely used because they are relatively inexpensive andhave compatibility with read-only optical disks.

Media such as CD-R representative of optical disks having the dyecontaining recording layer, for example, are in a laminated structurewhich has a dye containing recording layer and a reflective layer inorder on a transparent disk substrate along with a protective layer forcovering the dye containing recording layer and the reflective layer.Recording or reading are performed with a laser beam through thesubstrate.

In such CD-R, a power calibration area (PCA) for optimization of therecording power of the laser beam (OPC: Optimum Power Control) is set ina portion on the inner peripheral side with respect to the lead-in area,as shown in FIG. 11, for example (refer to Japanese Unexamined PatentPublication No. HEI 9-63061, for example). The PCA is divided into anOPC area and an OPC management area. Each of the areas is comprised ofone hundred partitions, and one partition is used in each area for oneOPC process. At this time, the partitions in the OPC area are used fromthe outer peripheral side to the inner peripheral side, whereas thepartitions in the OPC management area are used from the inner peripheralside to the outer peripheral side.

In the case of CD-R, when recording on the information recording area isperformed with a laser beam, various powers of the laser beam are usedto perform trial writing in the OPC area (for example, a partition a_(□)in FIG. 11), reading of the records written on trials are repeated, theoptimum power of the laser beam that can read most appropriately isdetermined, and the state of use of the OPC area such as the number oftimes the trial writing has been performed is recorded in the OPCmanagement area (for example, a partition b_(□) in FIG. 11).

Meanwhile, a recommended recording power value of the laser beam isbeforehand recorded in the medium, in general. However, since theoptimum power practically varies depending on the medium, it is said tobe preferable that the PCA as above is set in each medium to optimizethe power of the laser beam each time recording is performed on themedium.

DVD-R (single-sided, single-layer DVD-R), which is representative aswell, has a laminated structure in which a dye containing recordinglayer, a reflective layer and a protective layer covering them areformed in this order on a first transparent disk substrate, and aso-called dummy disk, which is a second disk substrate (which may betransparent or opaque) and a reflective layer formed on the second disksubstrate is formed on the protective layer through or not through anadhesive layer. Recording or reading are performed with a laser beamfrom one side of the disk through the first transparent disk substrate.The dummy disk may be of only a transparent or opaque disk substrate, ormay be provided with a layer other than the reflective layer.

Meanwhile, DVD+R has almost the same structure as DVD-R, description ofwhich will be hereinafter represented by DVD-R.

CD-R and DVD-R are optical disks using chemical changes in the dyerecording layer, onto which writing is possible only once (that is,rewriting is impossible). On the other hand, CD-RW and DVD-RW areoptical disks of the phase-change type using crystalline changes in therecording layer, onto which rewriting can be performed plural times. Insuch phase-change optical disks, protective layers are formed on andunder the recording layer, in general.

In order to largely increase the recording capacity of the opticalrecording medium, two single-sided DVD-Rs as above are bonded togetherto form a medium having two recording layers, which is known as adouble-sided DVD-R (double-sided, dual-layer DVD-R). Recording orreading are performed by irradiating a laser beam onto each of therecording layers from the both sides (that is, the laser beam is emittedfrom one side of the medium to perform recording and reading on arecording layer closer to this side, while the laser beam is emittedfrom the other side of the medium to perform recording or reading on theother recording layer closer to the other side).

Like the CD-R described above, a PCA for the OPC process is set in theknown single-sided DVD-R and double-sided DVD-R, as well.

With respect to optical recording media having a plurality of recordinglayers, there is, in these years, a demand for a single-sided incidenttype optical recording medium (for example, single-sided incidentdual-layer DVD-R) on which recording or reading can be performed on aplurality of recording layers by irradiating a laser beam from one sideso as to avoid an increase in size and complexity of therecording/reading apparatus, enable continuous reading from the pluralrecording layers, and improve the facility.

To meet the above demand, there has been proposed an optical recordingmedium (DVD-R) as shown in FIG. 12, for example. Namely, there has beenproposed a single-sided incident type DVD-R of the dual layer type(single-sided, dual-layered DVD-R) having two recording layers, forexample, as the single-sided incident type optical recording mediumhaving the structure below (refer to Japanese Unexamined PatentPublication No. HEI 11-66622).

For example, a single-sided incident type DVD-R of the dual layer typeof the laminated type is formed by laminating, on a firstlight-transmissible substrate 5, a first recording layer 12 made from anorganic dye on which information can be optically recorded byirradiating a laser beam for recording, a first reflective layer 13 madeof a semi-light-transmissible reflective film that can pass through apart of the laser beam for reading, an intermediate layer 11 that canpass through the laser beam for recording and the laser beam forreading, a second recording layer 12′ made from an organic dye on whichinformation can be optically recorded by irradiating the laser beam forrecording, a second reflective layer 13′ reflecting the laser beam forreading, and a second light-transmissible substrate 5′ in this order.

With the above structure, it is possible to record information on boththe first recording layer 12 and the second recording layer 12′ from oneside of the optical recording medium. In reading, it is possible to readout signals from one side of the medium as being an optical recordingmedium of the so-called dual-layer type.

In the case of an optical recording medium having two recording layerson which information is recorded by irradiating a laser beam from oneside, there is possibility that conditions of the recording or readingvary according to each recording layer because the recording on thesecond recording layer 12′ is performed through the first recordinglayer 12, the semi-light-transmissible reflective layer 13, and soforth.

Particularly, the complex refractive index of the first recording layer12 is changed according to whether or not information is recorded on thefirst recording layer 12, and thus the quantity of transmitted light ischanged. For this, there is possibility that the optimum recording powerto the second recording layer 12′ largely varies.

When data is recorded on each recording layer of an optical recordingmedium (particularly, a single-sided incident type DVD-R of the duallayer type) having a plurality of recording layers, it is necessary toperform the recording at the optimum recording power (optimum power) oneach recording layer in order to attain good recording on each recordinglayer.

When the OPC (Optimum Power control) is performed in an area on theinner peripheral side with respect to the data recording area on eachrecording layer to obtain the optimum power before the recording isperformed on each recording layer, the power of the laser diode (laserpower) is controlled to be the optimum power beforehand determined, datais then recorded.

When an electric current is supplied, the laser diode used as the lightsource of the recording light oscillates a laser power according to theelectric current. However, when the laser diode continuously oscillates,the temperature is increased, thus the laser power tends to be decreasedeven at the same electric current value.

When the temperature rises, the wavelength of the laser beam outputtedfrom the laser diode tends to shift toward the longer wavelength's side.Particularly, CD-R and DVD-R have the maximum absorbed wavelength on theshorter wavelength's side than the wavelength of the laser beam, thusthe absorption becomes smaller as the wavelength of the laser beamshifts to the longer wavelength. When the wavelength of the laser beam,which is the recording beam, shifts to the longer wavelength's side, therecording sensitivity deteriorates. Accordingly, a larger laser power isrequired for stable recording.

Further, the temperature of the laser diode itself changes according tothe magnitude of the laser power used for recording, the recording time,the ambient temperature, etc. This causes a change in the laser power.

Even if the electric current value of the laser diode is so set and thelaser power is so controlled as to provide the previously-determinedoptimum power, the laser power actually outputted may change due to achange in temperature of the laser diode, for example, which may makeexcellent recording difficult.

In the case where data is recorded in one recording layer and data iscontinuously recorded on the other recording layer, if the data isrecorded on the latter recording layer with a laser electric currentvalue corresponding to the optimum power beforehand determined, there ispossibility that the data is not recorded or the recording isinsufficient because the laser power is insufficient, which bringsfailure in excellent recording.

Particularly, when data is continuously recorded on plural recordinglayers, it is impossible to perform the OPC on each of the recordinglayers immediately before the recording is performed on each of therecording layer. For this reason, there is no other alternative but touse the optimum power determined in the OPC beforehand performed. It isthus impossible to cope with changes in temperature of the laser lightsource, which obstacles attainment of excellent recording in eachrecording layer.

DISCLOSURE OF INVENTION

In the light of the above problems, an object of the present inventionis to provide an optical recording medium having a plurality ofrecording layers on which information can be recorded by irradiating alaser beam from one side thereof, and a recording method and a recordingapparatus for the optical recording medium which can determine anoptimum recording power to each of the recording layers.

The recording method and the recording apparatus for the opticalrecording medium of this invention are aimed at accurately adjusting therecording power used when data is recorded on each of the layers evenwhen the recording power is changed due to a change in temperature ofthe laser light source, for example, thereby accomplishing goodrecording on each of the recording layers.

The optical recording medium according to this invention has a pluralityof recording layers on which information can be recorded by irradiatinga laser beam from one side thereof, each of the recording layersincluding and a power calibration area for optimizing the intensity ofthe laser beam.

It is preferable that the power calibration area is located at the innerperipheral side and/or the outer peripheral side of an informationrecording area of the recording layer.

The optical recording medium according to this invention has anoptical-transmissible first substrate, a first recording layer disposedon the first substrate, on which information can be recorded byirradiating a laser beam from the first substrate's side and a secondrecording layer disposed on the first recording layer, on whichinformation can be recorded by irradiating the laser beam. Each of thefirst recording layer and the second recording layer includes a powercalibration area for optimizing the intensity of the laser beam.

It is preferable that the power calibration areas of the first recordinglayer and the second recording layer are located at the inner peripheralside and/or the outer peripheral side of information recording areas ofthe first recording layer and the second recording layer, respectively.

It is preferable that the power calibration areas of the first recordinglayer and the second recording layer are set at the inner peripheralside of the information recording areas of the first recording layer andthe second recording layer, respectively, and recording of informationon the first recording layer and the second recording layer is performedfrom the inner peripheral side toward the outer peripheral side in theinformation recording areas.

It is preferable that the power calibration area of the first recordinglayer is set at one side of the inner peripheral side and the outerperipheral side of the information recording area, whereas the powercalibration area of the second recording layer is set at the other sideof the information recording area, and recording on the first recordinglayer and recording on the second recording layer are performed forwardopposite directions.

It is preferable that the power calibration area of the second recordinglayer has an area not covered with the power calibration area of thefirst recording layer.

It is preferable that a part of the first recording layer overlapping onthe power calibration area of the second recording area is in apreviously-recorded state.

It is preferable that recording of information on the first recordinglayer is performed before recording of information on the secondrecording layer.

It is preferable that a recommended recording power value for each ofthe recording layers is beforehand recorded.

A recording method for an optical recording medium according to thisinvention is a recording method for an optical recording medium having aplurality of recording layers, which comprises an OPC recording powersetting step of performing an optimum power control (hereinafterreferred to as an OPC) before recording on each of the plural recordinglayers to set an OPC recording power for each of the recording layers.

It is preferable that the recording method according to this inventionfurther comprises an initial recording power setting step of correctingan OPC recording power for another recording layer set at the OPCrecording power setting step based on a change in actual recording powerrelative to an OPC recording power for one recording layer set at theOPC power setting step to set a recording power to be used whenrecording another recording layer is performed.

It is preferable that a change in actual recording power is estimated onthe basis of the temperature of the laser light source at the initialrecording power setting step.

It is also preferable that a change in actual recording power isestimated on the basis of the quantity of reflected light from theoptical recording medium at the initial recording power setting step.

It is still also preferable that a change in actual recording power isestimated on the basis of the quantity of emitted light from the laserlight source at the initial recording power setting step.

It is still also preferable that a change in actual recording power isestimated on the basis of the laser current value set in a running OPCat the initial recording power setting step.

It is still also preferable that a change in actual recording power isestimated on the basis of the time period the laser beam is emitted atthe initial recording power setting step.

It is preferable that recording on one recording layer and recording onanother recording layer are continuously performed.

It is still preferable that the OPC recording power setting step isbeforehand performed on all of the recording layers before recording onthe optical recording medium, and the initial recording power settingstep is performed after recording on one recording layer beforerecording on another recording layer.

It is preferable that the OPC is performed on the inner peripheral sideand the outer peripheral side of each recording layer at the OPCrecording power setting step.

A recording apparatus for an optical recording medium is a recordingapparatus for an optical recording medium having a plurality ofrecording layers, which comprises a control arithmetic unit forperforming an optimum power control (hereinafter referred to as an OPC)before recording on each of the plural recording layers to set an OPCrecording power for each of the recording layers.

It is preferable that the control arithmetic unit corrects an OPCrecording power for another recording layer based on a change in actualrecording power relative to an OPC recording power for one recordinglayer to set a recording power to be used when recording on the latterrecording layer is started.

It is preferable that the control arithmetic unit estimates a change inactual recording power on the basis of the temperature of the laserlight source.

Alternatively, the control arithmetic unit estimates a change in actualrecording power on the basis of the quantity of reflected light from theoptical recording medium.

Still alternatively, the control arithmetic unit estimates a change inactual recording power on the basis of the quantity of emitted lightfrom the laser light source.

Still alternatively, the control arithmetic unit estimates a change inactual recording power on the basis of the laser current value set in arunning OPC.

Still alternatively, the control arithmetic unit estimates a change inactual recording power on the basis of the time period the laser beam isemitted.

The control arithmetic unit continuously performs recording on onerecording layer and recording on another recording layer.

Further, the control arithmetic unit beforehand sets an OPC recordingpower for each of all the recording layers before recording on theoptical recording medium, and sets a recording power to be used at thetime of start of recording on the another recording layer afterrecording on the one recording layer before recording on the anotherrecording layer.

The control arithmetic unit performs the OPC on the inner peripheralside and the outer peripheral side of each of the recording layers.

It is preferable that the present invention is applied to an opticalrecording medium in which the recording layers are dye containingrecording layers.

According to this invention, in an optical recording medium on whichinformation is recorded on a plurality of recording layers byirradiating a laser beam from one side thereof, a power calibration areafor optimizing the intensity of the laser beam is set on each of therecording layers so that an optimum recording power for each of therecording layers is determined.

Accordingly, it becomes possible to accurately adjust the recordingpower to be used when data is recorded on each of the recording layers,thereby to accomplish good recording on each of the layers.

An advantage of the recording method and recording apparatus for theoptical recording medium according to this invention is that therecording power to be used at the time of recording of data on each ofthe recording layers can be accurately adjusted even when the recordingpower is changed due to, for example, a change in temperature of thelaser light source, which allows good recording on each of the recordinglayer. As a result, when recording is continuously performed on aplurality of recording layers of an optical recording medium having theplural recording layers, for example, it is possible to perform goodrecording on each of the recording layers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram typically showing an optical recording medium (oftype 1) according to a first embodiment of this invention;

FIG. 2 is a diagram typically showing an optical recording medium (oftype 2) according to the first embodiment of this invention;

FIG. 3 is a diagram typically showing the whole structure of a recordingapparatus for the optical recording medium according to the firstembodiment of this invention;

FIG. 4 is a flowchart for illustrating a recording method for theoptical recording medium according to the first embodiment of thisinvention;

FIG. 5(A) is an area structure diagram for illustrating an areastructure of the optical recording media (of the type 1 and the type 2),and optimization of a recording power according to the first embodimentof this invention;

FIG. 5(B) is an enlarged diagram of essential parts in FIG. 5(A);

FIG. 6(A) is an area structure diagram for illustrating an areastructure of the optical recording media (of the type 1 and the type 2),and optimization of a recording power according to a second embodimentof this invention;

FIGS. 6(B) and 6(C) are enlarged diagrams of essential parts in FIG.6(A);

FIG. 7(A) is an area structure diagram for illustrating an areastructure of the optical recording media (of the type 1 and the type 2),and optimization of a recording power according to a third embodiment ofthis invention;

FIGS. 7(B) and 7(C) are enlarged diagrams of essential parts in FIG.7(A);

FIG. 8 is a flowchart for illustrating a recording method for theoptical recording medium according to a fourth embodiment of thisinvention;

FIGS. 9(A) and 9(B) are diagrams for illustrating changes in lasercurrent value and recording power occurring when a running OPC isperformed while data is recorded in the optical recording mediumaccording to the fourth embodiment of this invention;

FIGS. 10(A) and 10(B) are diagrams for illustrating changes in lasercurrent value and recording power occurring when the running OPC is notperformed while data is recorded in the optical recording mediumaccording to the fourth embodiment;

FIG. 11 is a diagram typically illustrating an area structure of a knownoptical recording medium (CD-R), and optimization of a recording power;and

FIG. 12 is a diagram typically showing a known dual-layer opticalrecording medium.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

[A] First Embodiment

A recording method and a recording apparatus for an optical recordingmedium according to this embodiment can be applied to all opticalrecording media having a plurality of recording layers.

For example, it is preferable that the recording method and therecording apparatus of this embodiment are used to record data(information) in a single-sided incident type optical recording medium(single-sided incident type DVD), which has a plurality of recordinglayers, and in which data can be recorded on and read from the recordinglayers by irradiating a beam (laser beam) from one side thereof.

Particularly, the present invention is more effective when it is appliedto an optical recording medium having dye containing recording layersbecause the recording sensitivity of the dye containing recording layerof, for example, a single-sided incident type DVD-R largely changes dueto a change in wavelength of the laser beam.

As the single-sided incident type optical recording media (opticaldisks), there are single-sided incident type DVD-Rs (single-sided,dual-layer DVD-R; single-sided, dual-layer DVD recordable disk) of thedual-layer type having two dye containing recording layers, for example,which are classified into the laminated type and the bonded type.

[1] Laminated Structures of Optical Recording Media

First, description will be made of optical recording media (dual-layer,single-sided incident-type DVD-Rs of the laminated type) of two typeshaving different laminated structures according to this embodiment.

[1-1] Optical Recoding Medium of Type 1

FIG. 1 is a sectional view of a typical optical recording medium(type 1) according to this embodiment.

The optical recording medium of the type 1 according to this embodimenthas, as shown in FIG. 1, a first recording layer (first recording layer,first dye containing recording layer) 2 containing a dye, asemitransparent reflective layer (hereinafter referred to as asemitransparent reflective layer, first reflective layer) 3, anintermediate resin layer (intermediate layer) 4, a second recordinglayer (second recording layer, second dye containing recording layer) 5containing a dye, a reflective layer (second reflective layer) 6, anadhesive layer 7 and a second substrate (second substrate) 8 in thisorder on a disk-shaped transparent (light-transmissible) first substrate(first substrate, first light-transmissible substrate) 1. Optical beams(laser beams) are emitted from the side of the first substrate 1 toperform recording or reading.

In this embodiment, “transparent (light-transmissible)” signifies“transparent (light-transmissible) to optical beams used for recordingon or reading from the optical recording medium.” Transparent(light-transmissible) layers include a layer which absorbs more or lessthe optical beams used for recording or reading. For example, when thelayer has a transmittance of not less than 50 percent (preferably notless than 60 percent) to the wavelength of an optical beam used forrecording or reading, the layer is considered to be light-transmissible(transparent).

Concavities and convexities (lands and grooves) are formed on thetransparent first substrate 1 and the intermediate resin layer 4. Arecording track is formed with the concavity and/or the convexity.Incidentally, the recording track may be formed with either theconcavity or the convexity. Generally, it is often that the recordingtrack 11 on the first substrate 1 is formed with the convexity withrespect to the direction of the incident light beam, and the recordingtrack 12 on the intermediate resin layer 4 is formed with the convexitywith respect to the direction of the incident light beam, as well. Inthis invention, the concavity and convexity are defined with respect tothe direction of incident light beams used for recording or readingunless not specifically mentioned.

These recording tracks 11 and 12 are made slightly snake in the radialdirection at predetermined amplitude and frequency (this called“wobble”). Isolated pits (address pits) are formed according to acertain rule on the land between the recording tracks 11 and 12 (thiscalled “land pre-pits, LPP; Land Pre-Pit). Address information may bebeforehand recorded with the land pre-pits. Incidentally, concave orconvex pre-pits may be sometimes formed as needed other than the landpre-pits. It is also possible to reverse the direction of the wobble ormodulate the frequency, thereby to record information.

Next, each of the layers will be described.

(1) With Respect to First Substrate 1

It is desirable that the first substrate 1 has excellent opticalcharacteristics, that is, the first substrate 1 is transparent, hassmall birefringence, and so force. It is also desirable that the firstsubstrate 1 has excellent molding properties, that is, the firstsubstrate 1 can be readily formed in injection molding. When the firstsubstrate 1 has small hygroscopicity, such property is desirable becausethe warping can be decreased.

Further, it is desirable that the first substrate 1 has shape stabilityso that the optical recording medium has some degree of rigidity. Whenthe second substrate 2 has sufficient shape stability, the firstsubstrate 1 is not required to have large shape stability.

As such material, it is possible to use resins such as acrylic resins,methacrylic resins, polycarbonate resin, polyolefin resins(particularly, amorphous polyolefin), polyester resins, polystyreneresin, epoxy resin, and so forth, and glass. Alternatively, it ispossible to provide a resin layer made from a radiation-setting resinsuch as a photo-setting resin or the like on the substrate made fromglass or the like. Incidentally, “radiation” is a general term for light(ultraviolet radiation, visible radiation, infrared ray, etc.), electronbeams, and the like.

Meanwhile, polycarbonate is preferable from the viewpoint of opticalproperties, high productivity such as molding properties and the like,cost, low hygroscopicity, shape stability, etc. From the viewpoint ofchemical resistance, low hygroscopicity and the like, amorphouspolyolefin is preferable. From the viewpoint of high-speedresponsibility and the like, a glass substrate is preferable.

The first substrate 1 is preferably thin. It is preferable that thefirst substrate 1 has a thickness of not more than 2 mm, more preferablynot more than 1 mm. The smaller the distance between the objective lensand the recording layer and the thinner the substrate, the smaller iscoma abberations, which is advantageous to increase the recordingdensity. To obtain sufficient optical properties, hygroscopicity,molding properties and shape stability, some degree of thickness isrequired. It is thus preferable that the thickness of the firstsubstrate 1 is generally not less than 10 μm, more preferably not lessthan 30 μm.

In order to well perform recording or reading on both of the firstrecording layer 2 and the second recording layer 5 in this opticalrecording medium, it is desirable to suitably adjust the distancebetween the objective lens and the both recording layers. For example,it is preferable to set the focus of the objective lens at an almostintermediate point between the both recording layers because accesses tothe both layers become easy.

More concretely, in a single-sided DVD-R system, the distance betweenthe objective lens and the recording layer is adjusted to be mostsuitable when the thickness of the substrate is 0.6 mm.

When this layer structure is compatible with a single-sided DVD-R, it ismost preferable that the first substrate 1 has a thickness obtained bysubtracting a half of the film thickness of the intermediate resin layer4 from 0.6 mm. If so, the approximately intermediate point between theboth layers is approximately 0.6 mm, thus the focusing servo control canbe readily performed on the both recording layers.

When another layer such as a buffer layer, a protective layer or thelike exists between the second recording layer 5 and the semitransparentreflective layer 3, it is most preferable that the first substrate 1 hasa thickness obtained by subtracting a half of a sum of the thicknessesof that layer and the intermediate resin layer 4 from 0.6 mm.

Concavities and convexities are formed spirally or concentrically on thefirst substrate 1 to form grooves and lands. Generally, with suchgrooves and lands as being recording tracks, information is recorded onor read from the first recording layer 2. In the case of a so-called DVDdisk on which recording or reading are performed by condensing a laserbeam having a wavelength of 650 nm with an objective lens having anumerical aperture of 0.6 to 0.65, the first recording layer 2 isgenerally formed in coating, so that the film of the second recordinglayer 2 is thick at the grooves, which is suitable for recording orreading.

In this optical recording medium, it is preferable that the groove ofthe first substrate 1, that is, the convexity with respect to thedirection of the incident light beam, is used as the recording track 11.Here, the concavity and the convexity are portions recessed andprojecting in relation with the direction of the incident light beam.Generally, the width of the groove is about 50 to 500 nm, and the depthof the groove is about 10 to 250 nm. When the recording track is spiral,the track pitch is preferably about 0.1 to 2.0 μm. The first substrate 1may have concave or convex pits such as land pre-pits or the like asrequired.

From the viewpoint of cost, it is preferable to manufacture thesubstrate having such concavities and convexities in injection moldingfrom a stamper having concavities and convexities. When a resin layermade of a radiation-setting resin such as a photo-setting resin or thelike is formed on the substrate made from glass or the like, a concavityor a convexity such as a recording track or the like may be formed onthe resin layer.

(2) With Respect To First Recording Layer 2

Generally, the sensitivity of the first recording layer 2 is almostequivalent to that of the recording layer used in a single-sidedrecording medium (for example, CD-R, DVD-R, DVD+R) or the like.

In order to realize a good recording/reading performance, it ispreferable that the first recording layer 2 contains a low-exothermaticdye having high refractive index.

Further, a combination of the first recording layer 2 and thesemitransparent reflective layer 3 is preferably within appropriateranges of the reflection, transmission and absorption of light, wherebythe recording sensitivity is improved and the thermal interference atthe time of recording is decreased.

As such organic dye material, there are macrocyclic azaannulene typedyes (phtalocyanine dye, naphtalocyanine dye, porphyrin dye, etc.),pyrromethene type dyes, polymethine type dyes (cyanine dye, merocyaninedye, squalirium dye, etc.) anthoraquinone type dyes, azulenium typedyes, metal complex azo type dyes, metal complex indoaniline type dyes,etc.

Among the above various organic dyes, metal complex azo type dyes arepreferable because they have excellent recording sensitivity, durabilityand light resistance. Particularly, a compound represented by thefollowing general formula (□) or (□) is preferable:

(where rings A¹ and A² are nitrogen-containing aromatic heterocyles,each of which can independently have a substituent; rings B¹ and B² arearomatic rings, each of which can independently have a substituent; andX is an alkyl group having carbon number 1 to 6 substituted with atleast two fluorine atoms). An organic dye used in the recording layer(incidentally, “recording layer” hereinafter signifying both the firstrecording layer 1 and the second recording layer 2 unless specificallymentioned) of this optical recording medium preferably has the maximumabsorption wavelength λ max within a range from the visible rays to thenear infrared rays of approximately 350 to 900 nm, and is a dye compoundsuited to recording with a laser of blue to near microwave. Morepreferable is a dye suited to recording with a near infrared laser(typically at 780 nm, 830 nm, etc.) used generally for CD-R, a red laser(typically at 635 nm, 650 nm, 680 nm, etc.) at about a wavelength of 620to 690 nm used for DVD-R, or a so-called blue laser at a wavelength of410 nm or 515 nm.

It is possible to use one kind of dye, or mix two or more the same ordifferent kinds of dyes and use them. Further, it is possible to usetogether dyes suited for recording with a recording beam at a pluralityof wavelengths to realize an optical recording medium coping withrecording with a laser beam in a plurality of wavelength bands.

The recording layer may contain a transition metal chelate compound (forexample, acetylacetonato chelate, bisphenyldithiol, salicylaldehydeoxime, bisdithio-α-diketone or the like) as a singlet oxygen quencher inorder to stabilize the recording layer or improve the light resistance,or a recording sensitivity improving agent such as a metal systemcompound or the like in order to improve the recording sensitivity.Here, the metal system compound is that a metal such as a transitionmetal or the like in the form of atom, ion, cluster or the like iscontained in a compound. As such metal system compound, there are, forexample, organometallic compounds such as ethylenediamine complexes,azomethine complexes, phenylhydroxyamine complexes, phenanthrolinecomplexes, dihydroxyazobenzene complexes, dioxime complexes,nitrosoaminophenol complexes, phyridyltriazine complexes,acetylacetonato complexes, metallocene complexes, porphyrin complexes,and the like. There is no limitation with respect to the metal atom, buta transition metal is preferable.

Further, a binder, a leveling agent, an antiforming agent and the likemay be together used to make the recording layer of this opticalrecording medium as required. As a preferable binder, there arepoly(vinyl alcohol), poly(vinyl pyrrolidone), nitrocellulose, celluloseacetate, ketone resins, acrylic resins, polystyrene resins, urethaneresins, poly(vinyl butyral), polycarbonate, polyolefin, etc.

The film thickness of the recording layer is not specifically limitedbecause the suited film thickness differs according to the recordingmethod or the like. However, in order to obtain sufficient modulationamplitude, the film thickness is preferably not less than 5 nm, morepreferably not less than 10 nm, and specifically preferably not lessthan 20 nm, in general. However, the recording layer is required not tobe excessively thick in order to appropriately pass through the light inthis optical recording medium. Accordingly, the film thickness of therecording layer is generally not larger than 3 μm, preferably not largerthan 1 μm, and more preferably not larger than 200 nm. The filmthickness of the recording layer differs from the groove to the land. Inthis optical recording medium, the film thickness of the recording layeris at the groove of the substrate.

As the method of deposition of the recording layer, there can be applieda thin film deposition generally performed such as vacuum evaporation,sputtering method, doctor blade method, cast method, spin coating,dipping method or the like. From the standpoint of productivity andcost, spin coating is preferable. Vacuum evaporation is more preferablethan coating method because it can yield a recording layer having eventhickness.

When the deposition is performed in spin coating, the rotation speed ispreferably 10 to 15000 rpm. After the spin coating, a process of heatingor applying solvent vapor or the like may be performed.

As a coating solvent used when the recording layer is formed in acoating method such as doctor blade method, cast method, spin coating,dipping method or the like, the type of solvent is not limited, thus anysolvent can be used so long as it does not attack the substrate. Forexample, there are ketone alcohol type solvents such as diacetonalcohol, 3-hydroxy-3-methyl-2-butanone and the like, cellosolve typesolvents such as methyl cellosolve, ethyl cellosolve and the like, chainhydrocarbon type solvents such as n-hexane, n-octane and the like, ringhydrocarbon type solvents such as cyclohexane, methylcyclohexane,ethylcyclohexane, dimethylcyclohexane, n-butylcyclohexane,tert-butylcyclohexane, cyclooctane and the like, perfluoroalkylalcoholtype solvents such as tetrafluoropropanol, octafluoropentanol,hexafluorobutanol and the like, hydroxy carboxylic acid ester typesolvents such as methyl lactate, ethyl lactate, methyl2-hydroxyisobutyric acid and the like, etc.

In the case of vacuum evaporation, an organic dye is put in a crucibledisposed inside a vacuum chamber, along with recording layer componentssuch as various additives and the like as required, for example, theinside of the vacuum chamber is evacuated to about 10⁻² to 10⁻⁵ Pa by anappropriate vacuum pump, after that, the crucible is heated to vaporizethe recording layer components, and the recording layer components aredeposited on the substrate placed opposite to the crucible, whereby therecording layer is formed.

(3) With Respect To Semitransparent Reflective Layer 3

The semitransparent reflective layer 3 is a reflective layer having somedegree of light transmittance. Namely, the semitransparent reflectivelayer 3 is a reflective layer which has small light absorption, a lighttransmittance of not less than 40 percent, and appropriate lightreflectance (of not less than 30 percent, in general). For example, byproviding a thin metal film having high reflectance, it is possible togive appropriate transmittance. It is desirable that the semitransparentreflective layer 3 have some degree of corrosion resistance. Further, itis desirable that the semitransparent reflective layer 3 hasshutting-off properties so that the first recording layer 2 is notaffected by leaking of the upper layer (here the intermediate resinlayer 4) of the semitransparent reflective layer 3.

To secure high transmittance, the thickness of the semitransparentreflective layer 3 is preferably not larger than 50 nm, in general. Thethickness of the semitransparent reflective layer 3 is more preferablynot larger than 30 nm, and still more preferably not larger than 20 nm.However, the semitransparent reflective layer 3 is required to be thickto some degree in order to avoid an effect of the upper layer of thesemitransparent reflective layer 3 on the first recording layer 2. Thus,the thickness of the semitransparent reflective layer 3 is generally notless than 3 nm, and more preferably not less than 5 nm.

As the material of the semitransparent reflective layer 3, it ispossible to use, solely or in the form of alloy, metals and semimetalssuch as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Pd, Mg, Se, Hf, V, Nb, Ru,W, Mn, Re, Fe, Co, Rh, Ir, Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Biand rare earth metals, which have appropriately high reflectance at thewavelength of the reading beam. Among them, Au, Al and Ag have highreflectance, thus are suitable as the material of the semitransparentreflective layer 3. The semitransparent reflective layer 3 may containother component other than the above as being the main component.

A material containing Ag as the main component is particularlypreferable because of its low cost and high reflectance. Here, the maincomponent signifies a material contained not less than 50 percent.

Since the semitransparent reflective layer 3 has thin film thickness,large crystal grains of the film cause reproduction noise. Thus, it ispreferable to use a material having small crystal grains. Since puresilver tends to have large crystal grains, it is preferable to use Ag asin the form of alloy.

Particularly, it is preferable to contain Ag as the main component, and0.1 to 15 atomic percent of at least one element selected from the groupconsisting of Ti, Zn, Cu, Pd, Au and rare earth metals. When two or moreof Ti, Zn, Cu, Pd, Au and rare earth metals are contained, each of thesemay be 0.1 to 15 atomic percent. However, the sum of these is preferably0.1 to 15 atomic percent.

A particularly preferable alloy composition is one that contains Ag asthe main component, 0.1 to 15 atomic percent of at least one elementselected from the group consisting of Ti, Zn, Cu, Pd and Au, and 0.1 to15 atomic percent of at least one rare earth element. Among the rareearth metals, neodymium is particularly preferable. In more concrete,AgPdCu, AgCuAu, AgCuAuNd, AgCuNd, etc. are preferable.

As the semitransparent reflective layer 3, a layer made from only Au ispreferable because it has small crystal grains and corrosion resistance,but it is more expensive than an Ag alloy.

Alternatively, it is possible to use a layer made from Si as thesemitransparent reflective layer 3.

It is possible to stack, one on the other, a thin film having lowreflectance and a thin film having high reflectance both made frommaterials other than metals to form multi-layers, and use them as thereflective layer.

As a method for forming the semitransparent reflective layer 3, therecan be applied, for example, sputtering, ion plating, chemicalevaporation, vacuum evaporation, etc. It is possible to provide aninorganic or organic intermediate layer and an adhesive layer betweenthe first substrate 1 and the first recording layer 2, and/or, the firstrecording layer 2 and the semitransparent reflective layer 3 in order toimprove the reflectance, the recording performance and the adhesiveproperties. For example, it is possible that an intermediate layer (oran adhesive layer), the first recording layer 2, and an intermediatelayer (or the adhesive layer) and the semitransparent reflective layer 3are stacked in this order on the first substrate 1 to provide theintermediate layer (or the adhesive layer) between the first substrate 1and the first recording layer 2, and to provide the intermediate layer(or the adhesive layer) between the first recording layer 2 and thesemitransparent reflective layer 3.

(4) With Respect to Intermediate Resin Layer 4

The intermediate resin layer (resin layer) 4 is required to betransparent, and to allow grooves and pits to be formed thereon withconcavities and convexities. It is preferable that the intermediateresin layer 4 has strong adhesion, and small shrinkage factor at thetime that the intermediate resin layer 4 hardens and adheres, whichgives stability to the shape of the medium.

It is desirable that the intermediate resin layer 4 is made from amaterial that does not damage the second recording layer 5. Theintermediate resin layer 4 is easily compatible with the secondrecording layer 5 because the intermediate resin layer 4 is generallymade from a resin. For this, it is desirable to provide a buffer layerto be described later between the intermediate resin layer 4 and thesecond recording layer 5 in order to prevent the intermediate resinlayer 4 from dissolving the second recording layer 5 and from givingdamage thereto.

Further, it is desirable that the intermediate resin layer 4 is madefrom a material that does not damage the semitransparent reflectivelayer 3. It is possible to provide a buffer layer to be described laterbetween the both layers in order to avoid the damage.

In this optical recording medium, it is preferable to accurately controlthe film thickness of the intermediate resin layer 4. The film thicknessof the intermediate resin layer 4 is preferably not less than 5 μm, ingeneral. It is necessary to provide a certain degree of distance betweenthe two recording layers in order to perform the focusing servo controlseparately on the two recording layers. The film thickness of theintermediate resin layer 4 is required to be generally not less than 5μm, and preferably not less than 10 μm although it depends on thefocusing servo mechanism. Generally, the distance between the tworecording layers can be smaller as the objective lens has a largernumerical aperture. However, when the intermediate resin layer 4 isexcessively thick, it takes a long time to adjust the focusing servo tothe two recording layers and the objective lens has to be moved for along distance, which is thus undesirable. Further, an excessively thicklayer requires a long time to harden, which leads to a decrease inproductivity. Accordingly, the film thickness of the intermediate resinlayer 5 is preferably not larger than 100 μm.

Spiral or concentric concavities and convexities are formed on theintermediate resin layer 4 to form grooves and lands. Generally, suchgrooves and lands are used as recording tracks to record or readinformation in or from the second recording layer 5. Since the secondrecording layer 5 is formed in coating, the film thereof is thick at thegroove, thus suits for recording or reading. In this optical recordingmedium, it is preferable to use the groove of the intermediate resinlayer 4, that is, the convex portion to the direction of the incidentlight beam, as the recording track 12. Here, the concave portion and theconvex portion are a concave portion and a convex portion with respectto the direction of the incident light beam. Generally, the width of thegroove is about 50 to 500 nm, and the depth of the same is about 10 to250 nm. When the recording track is spiral, the track pitch ispreferably about 0.1 to 2.0 μm. Concave or convex pits such as landpre-pits may be formed as required.

It is preferable from the viewpoint of the cost that such concavitiesand convexities are manufactured by transferring the concavities andconvexities from a resin stamper or the like having the concavities andconvexities to a setting resin such as a photo-setting resin, andhardening the resin. Hereinafter, such method will be occasionallyreferred to as 2P method (Photo Polymerization method).

As the material of the intermediate resin layer 4, available areradiation setting resins such as thermoplastic resins, thermosettingresins, electron beam setting resins, ultraviolet ray-curable resins(including retarded-curable type), etc., for example. Incidentally,“radiation” is a general term for light (ultraviolet rays, visible rays,infrared rays, etc.), electron beams, and so forth.

The intermediate resin layer 4 can be formed by dissolving athermoplastic resin, thermosetting resin or the like in an appropriatesolvent to prepare a coating liquid, applying the liquid, and drying(annealing) the liquid. In the case of a ultraviolet curable resin, theintermediate resin layer 4 can be formed by dissolving the resin as itis or dissolving the resin in an appropriate solvent to prepare acoating liquid, coating the coating liquid, and radiating ultravioletrays to cure the resin. There are various types of ultravioletray-curable resins. However, any one of them can be used so long as itis transparent. One of these materials can be used or some of them canbe mixed together to be used. Not only single layer but also multiplelayers are applicable.

As the coating method, a coating method such as spin coating, castmethod or the like is applicable, like the recording layer. Among them,spin coating is preferable. A resin having high viscosity can be coatedin screen printing or the like. Use of a ultraviolet ray-curable resinthat liquidizes at a temperature of 20 to 40° C. is preferable becauseno solvent is necessary to coat the resin. It is preferable to preparethe resin so that the viscosity thereof is 20 to 4000 mpa□s.

As the ultraviolet ray-curable adhesives, there are radical typeultraviolet ray-curable adhesives and cation type ultravioletray-curable adhesives, both of which are usable.

As the radical type ultraviolet setting adhesives, all the knowncompositions are available. A composition containing an ultravioletray-curable compound and a photopolymerization initiator as essentialingredients is used. As the ultraviolet ray-curable compound,monofunctional (meta) acrylate or multi functional (meta) acrylate isavailable as a polymeric monomer ingredient. These can be used solely,or two or more kinds of them can be used together. In this invention,acrylate and metaacrylate will be together referred to as(meta)acrylate.

For example, the followings are the polymeric monomers that can be usedfor this optical recording medium. As monofunctional (meta) acrylate,there is, for example, (meta)acrylate or the like having, as thesubstituent, a group of methyl, ethyl, propyl, butyl, amyl,2-ethylhexyl, octyl, nonyl, dodecyl, hexadecyl, octadecyl, cyclohexyl,benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl,tetrahydrofurfuryl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl,3-chloro-2-hydroxypropyl, dimethylaminoethyl, diethylaminoethyl,nonylphenoxyethyltetrahydrofurfuryl, caprolactone denaturatedtetrahydrofurfuryl, isobornyl, dicyclopentanyl, dicyclopentenyl,dicyclopentenyloxyethyl, or the like.

As the multifunctional (meta)acrylates, there are di(meta)acrylates of1,3-butylenegycol, 1,4-butanediol, 1,5-pentanediol,3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol,1,8-octanediol, 1,9-nonanediol, tricyrodecandimethanol, ethylene glycol,polyethylene glycol, propylene glycol, dipropylene glycol, tripropyleneglycol, polypropylene glycol and the like, di(meta)acrylate oftris(2-hydroxyethyl)isocyanurate, di(meta)acrylate of diole obtained byadding 4 or more moles of ethylene oxide or propylene oxide to 1 mole ofneopentyl glycol, di(meta)acrylate of diole obtained by 2 moles ofethylene oxide or propylene oxide to 1 mole of bisphenol A, di ortri(meta)acrylate of triol obtained by adding 3 or more moles ofethylene oxide or propylene oxide to trimethylolpropane,di(meta)acrylate of diol obtained by adding 4 or more moles of ethyleneoxide or propylene oxide to 1 mole of bisphenol A,trimethylolpropanetri(meta)acrylate, pentaerythritoltri(meta)acrylate,poly(meta)acrylate of dipentaerythritol, ethylene oxide denaturatedphospholic acid (meta)acrylate, ethylene oxide denaturated alkylatedphospholic acid (meta)acrylate, etc.

One that can be used together with polymeric polymer is polyester(meta)acrylate, polyether (meta)acrylate, epoxy(meta)acrylate, urethane(meta) acrylate or the like, as polymeric oligomer.

As a photopolimerization initiator used for this optical recordingmedium, any one of the known initiators that can harden a usedultraviolet ray-curable compound represented by polymeric oligomerand/or polymeric monomer can be used. As the optical polymerizationinitiator, the molecular fission type or the hydrogen abstraction typeis suitable.

As such photopolymerization initiator, suitably used are bensoinisobutyl ether, 2,4-diethylthioxanthone, 2-isoproplythioxanthone,benzyl, 2,4,6-trimethylbenzoyldiphenylphosphineoxide,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1-one,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpenthylphosphinoxide, etc. Asthe molecular fission type other than these,1-hydroxycyclohexylphenylketone, benzoinethylether, benzyldimethylketal,2-hydroxy-2-methyl-1-phenylpropane-1-one,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one,2-methyl-1-(4-methylthiophenyl)-2-morphorinopropane-1-one, and the likecan be together used. Further, benzophenone, 4-phenylbenzophenon,isophthalphenone, 4-benzoyl-4′-methyl-diphenylsulfide or the like, whichare photopolimerization initiator of the molecular abstraction type, canbe together used.

As the sensitizer to the photopolymerization initiator, amine that doesnot cause the addition reaction with the above polymeric component, suchas trimethylamine, methyldimethanolamine, triethanolamine,p-diethylaminoacetophenone, p-dimethylaminoethylbenzoate,p-dimethylaminoisoamylbenzoate, N,N-dimethylbenzylamine,4,4′-bis(diethylamino)benzophenone or the like. It is preferable toselect and use one of the above photopolymerization initiators andsensitizers which has excellent solubility to the ultravioletray-curable compound and does not hinder the ultraviolet raytransmissivity.

As the cation type ultraviolet ray-curable adhesive, all the knowncompositions can be used. Epoxy resins containing a photopolimerizationinitiator of the cation polymerization type correspond to this. As photoinitiators of the cation polymerization type, there are sulfonium salts,iodonium salts, diazonium salts, etc.

As examples of iodonium salts, there are diphenyliodoniumhexafluorophosphate, diphenyliodonium hexafluoroantimonate,diphenyliodonium tetrafluoroborate, diphenyliodoniumtetrakis(pentafluorophenyl) borate, bis(dodecylphenyl)iodoniumhexafluorophosphate, bis(dodecylphenyl)iodonium hexafluoroantimonate,bis(dodecyl)iodonium tetrafluoro borate, bis(dodecylphenyl)iodoniumtetrakis(pentafluorophenyl)borate,4-methylphenyl-4-(1-methylethyl)phenyliodonium hexafluorophosphate,4-methylphenyl-4-(1-methylethyl)phenyliodonium hexafluoroantimonate,4-methylphenyl-4-(1-methylethyl)phenyliodonium tetrafluoroborate,4-methylphenyl-4-(1-methylethyl)phenyliodoniumtetrakis(pentafluorophenyl)borate, etc.

As the epoxy resin, any one of bisphenol A-epichlorohydrin type,alicylic epoxy, long-chain aliphatic type, brominated epoxy resin,glycidyl ester type, glycidyl ether type, heterocyclic system, etc. isavailable.

As the epoxy resin, it is preferable to use one that has small contentsof liberated free chlorine and chlorine ions in order to avoid the resinfrom damaging the reflective layer. The quantity of chlorine ispreferably not larger than 1 wt %, and more preferably not larger than0.5 wt %.

A rate of the cation polymerization type photo-initiator to 100 parts byweight of the cation type ultraviolet ray-curable resin is generally 0.1to 20 parts by weight, and preferably 0.2 to 5 parts by weight. In orderto use more effectively the wavelengths in the near infrared ray regionor the visible radiation region in the wavelength band of theultraviolet ray source, it is possible to use together a known opticalsensitizer. As such optical sensitizer, there are anthracene,phenotiazine, benzylmethylketal, benzophenone, acetophenone, etc.

In order to improve various properties of the ultraviolet ray-curableadhesive, it is possible to add, as other additives, a thermalpolymerization inhibitor, an antioxidant represented by hindered phenol,hindered amine, phosphite, etc., a plasticizer, a silane coupling agentrepresented by epoxysilane, mercaptosilane, (meta)acrylsilane, etc., asrequired. Among them, one that has excellent solubility to theultraviolet ray-curable compound and does not hinder the ultraviolet raytransmissiveness is selected and used.

(5) With Respect to Second Recording Layer 5

The second recording layer 5 generally has higher sensitivity than arecording layer used for a single-sided recording medium (for example,CD-R, DVD-R, DVD+R) and the like. In this optical recording medium,since the power of an incident optical beam is divided by the presenceof the semitransparent reflective layer 3 or the like, and distributedfor recording in the first recording layer 2 and the recording in thesecond recording layer 5, recording is performed with a half of thepower. Accordingly, the second recording layer 5 is required to havespecifically high sensitivity.

For the purpose of realization of excellent recording/readingperformance, it is desirable that the dye develops a little heat and haslarge refractive index.

Further, it is desirable that a combination of the second recordinglayer 5 and the reflective layer 6 provides appropriate ranges ofreflection and absorption of the light. Whereby, the recordingsensitivity can be increased and the thermal interference at the time ofrecording can be diminished.

The materials and deposition method of the second recording layer 5 arealmost the same as the first recording layer 2, thus only thedifferences between them will be hereinafter described.

The film thickness of the second recording layer 5 is not specificallylimited because the suitable film thickness differs according to therecording method, etc. In order to obtain sufficient modulationamplitude, the film thickness of the second recording layer 5 ispreferably not less than 10 nm in general, more preferably not less than30 nm, and particularly preferably not less than 50 nm. However, thefilm is required not to be excessively thick in order to obtainappropriate reflectance, the film thickness is generally not larger than3 μm, preferably not larger than 1 μm, and more preferably not largerthan 200 nm.

The materials used for the first recording layer 2 and the secondrecording layer 5 may be the same or may differ from each other.

(6) With Respect to Reflective Layer 6

The reflective layer 6 is required to have high reflectance. It isdesirable that the reflective layer 6 is highly durable.

In order to secure high reflectance, the thickness of the reflectivelayer 6 is preferably not less than 20 nm, in general, more preferablynot less than 30 nm, and further preferably not less than 50 nm. Inorder to shorten the tact time of the production and decrease the cost,it is preferable that the reflective layer 6 is thin to some degree.Accordingly, the film thickness is generally not larger than 400 nm, andmore preferably not larger than 300 nm.

As the material of the reflective layer 6, it is possible to use, solelyor in a form of alloy, metals having sufficiently high reflectance at awavelength of the reading light such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt,Ta and Pd, for example. Among them, Au, Al and Ag are suitable for thematerial of the reflective layer 6 because they have high reflectance.Other than these as the main compositions, the reflective layer 6 maycontain the followings as other components. As examples of the othercomponents, there are metals such as Mg, Se, Hf, V, Nb, Ru, W, Mn, Re,Fe, Co, Rh, Ir, Cu, Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi and rareearth metals, and semimetals.

A film containing Ag as the main component is particularly preferablebecause the cost thereof is low, it provides high reflectance and abeautiful white ground color when a print accepting layer to bedescribed later is further provided. Here, “main component” signifies acomponent whose rate of content is not less than 50 percent.

In order to secure high durability (high corrosion resistivity) of thereflective layer 6, it is preferable to use Ag in the form of alloyrather than as pure silver.

Among the alloys, an alloy that contains Ag as the main component andcontains 0.1 to 15 atomic percent of at least one element selected fromthe group consisting of Ti, Zn, Cu, Pd, Au and rare earth metals ispreferable. When the alloy contains two or more of Ti, Zn, Cu, Pd, Auand rare earth metals, each of them may be contained 0.1 to 15 atomicpercent. However, it is preferable that the sum of these is 0.1 to 15atomic percent.

A particularly preferable composition of the alloy is that Ag iscontained as the main component, 0.1 to 15 atomic percent of at leastone element selected from the group consisting of Ti, Zn, Cu, Pd and Auis contained, and 0.1 to 15 atomic percent of at least one rear earthelement is contained. Among rare earth elements, neodymium isparticularly preferable. More concretely, AgPdCu, AgCuAu, AgCuAuNd,AgCuNd or the like is preferable.

As the reflective layer 6, a layer made from only Au is preferablebecause its high durability (high corrosion resistance), but is moreexpensive than a layer made from only an Ag alloy.

It is possible to stack a thin film having low reflective index and athin film having high reflective index, both of which are made frommaterials other than metals, one on the other to form a multilayer, anduse it as the reflective layer 6.

As a method for forming the reflective layer 6, there are, for example,spattering, ion plating, chemical vapor deposition, vacuum evaporation,etc.

It is possible to provide a known inorganic or organic intermediatelayer or an adhesive layer on the upper surface and the lower surface ofthe reflective layer 6 in order to improve the reflectance, recordingperformance, adhesive properties and so forth.

(7) With Respect to Adhesive Layer 7

The adhesive layer 7 is not required to be transparent. High adhesionand small shrinkage of the adhesive layer 7 at the time that the layeris hardened and adhered brings stability of the shape of the medium,which is preferable.

It is preferable that the adhesive layer 7 is made from a material thatdoes not damage the reflective layer 6. It is possible to provide aknown inorganic or organic protective layer between the both layers inorder to avoid the damage on the reflective layer 6.

In this optical recording medium, the film thickness of the adhesivelayer 7 is preferably not less than 2 μm, in general. In order to obtainpredetermined adhesion, some degree of film thickness is required. Morepreferably, the film thickness of the adhesive layer 7 is not less than5 μm. Generally, it is preferable that the film thickness of theadhesive layer 7 is not larger than 100 μm in order to make the opticalrecording medium thin as much as possible. This is why a thick filmrequires a longer time to be hardened, which leads to a decrease in theproductivity.

The material of the adhesive layer 7 may be the same as the material ofthe intermediate resin layer 4, or may be a pressure sensitivedouble-sided tape or the like. By putting the pressure sensitivedouble-sided tape between the reflective layer 6 and the secondsubstrate 8 and pressing them, the adhesive layer 7 can be formed.

(8) With Respect to Second Substrate 8

It is preferable that the second substrate 8 has shape stability so thatthe optical recording medium has some degree of rigidity. Namely, it ispreferable that the second substrate 8 has high mechanical stability andlarge rigidity. It is also preferable that the second substrate 8 haslarge adhesion to the adhesive layer 7.

When the first substrate 1 does not have sufficient shape stability asabove, the second substrate 8 is particularly required to have largeshape stability. In this viewpoint, it is preferable that the secondsubstrate 8 has low moisture absorption. The second substrate 8 is notrequired to be transparent. The second substrate 8 may be a mirrorsubstrate, and is not required to have concavities and convexitiesthereon. Thus, the second substrate 8 is not always required to havegood transfer property in injection molding.

As such material, the same material as that used for the first substrate1 can be used. Other than this, there can be used an Al alloy substratecontaining Al as the main component such as an Al—Mg alloy or the like,an Mg alloy substrate containing Mg as the main component such as anMg—Zn alloy or the like, a substrate made from any one of silicon,titanium and ceramics, or a substrate made by combining them.

In the viewpoint of high productivity such as molding property and thelike, cost, low moisture absorption, shape stability, etc.,polycarbonate is preferable. In the viewpoint of chemical resistance,low moisture absorption, etc., amorphous polyolefin is preferable. Inthe viewpoint of high-speed responsibility, etc., a glass substrate ispreferable.

In order to give sufficient rigidity to the optical recording medium, itis preferable that the second substrate 8 is thick to some degree,having a thickness of not less than 0.3 mm. However, since a thinnersecond substrate 8 is more advantageous to make the recording/readingapparatus thinner, the thickness of the second substrate 8 is preferablynot larger than 3 mm, and more preferably not larger than 1.5 mm.

The second substrate 8 may be a mirror substrate not having concavitiesand convexities thereon. From the standpoint of easy production, it ispreferable that the second substrate 8 is manufactured in injectionmolding.

An example of a preferable combination of the first substrate 1 and thesecond substrate 8 is that the first substrate 1 and the secondsubstrate 8 are made from the same material, and have the samethickness. By doing so, the rigidity of the first substrate land thesecond substrate 8 are equivalent, which gives good balance. Whereby,the medium is prone not deform due to changes in environment, which ispreferable. In which case, it is preferable that the degrees anddirections of deformation of the both substrates brought when theenvironments change are in harmony.

As another preferable example of the combination, the first substrate 1is as thin as about 0.1 mm, whereas the second substrate 8 is as thickas about 1.1 mm. By doing so, the objective lens can easily approach therecording layer, whereby the recoding density is easily increased.Accordingly, this is preferable. In this case, the first substrate 1 maybe in sheet-like shape.

(9) With Respect to Other Layers

In this layered structure, another layer may be arbitrarily put in thelayers as required. Alternatively, it is possible to arbitrarily provideanother layer on the outermost surface of the medium. In concrete, it ispossible to provide a buffer layer as an intermediate layer between thesemitransparent reflective layer 3 and the intermediate resin layer 4,the intermediate resin layer 4 and the second recording layer 5, or thereflective layer 6 and the adhesive layer 7, for example.

The buffer layer is to prevent two layers from dissolving in each otherand prevent the two layers from blending to each other. The buffer layermay have another function than the function of preventing the dissolvingphenomenon. Further, still another intermediate layer may be put asrequired.

The material of the buffer layer is required to be immiscible with thesecond recording layer 5 or the intermediate resin layer 4, and beoptically transmittable to some degree. The known inorganic or organicmaterial can be used for the buffer layer. In the viewpoint of theproperties, an organic material is preferably used. For example, (1)metal or semiconductor, (2) oxide, nitride, sulfide, trisulfide,fluoride or carbide of metal or semiconductor, and (3) amorphous carbonor the like are available. Among these, a layer made from an almosttransparent dielectric substance, or a very thin metal layer (includingalloy) is preferable.

In concrete, oxides such as silicon oxide, particularly, silicondioxide, zinc oxide, cerium oxide, yttrium oxide and the like; sulfidessuch as zinc sulfide, yttrium sulfide and the like; nitrides such assilicon nitride and the like; silicon carbide; a mixture (trisulfide) ofan oxide and sulfur; and alloys to be described later are preferable. Amixture of silicon oxide and zinc sulfide at a ratio of approximately30:70 to 90:10 (weight ratio) is preferable. A mixture (Y₂O₂S—ZnO) ofsulfur, yttrium dioxide and zinc oxide is also preferable.

As the metal or alloy, silver or an alloy that contains silver as themain component and 0.1 to 15 atomic percent of at least one elementselected from the group consisting of titanium, zinc, copper, palladiumand gold is preferable. An alloy that contains silver as the maincomponent and 0.1 to 15 atomic percent of at least one rare earthelement is preferable, as well. As the rare earth element, neodymium,praseodymium, cerium or the like is preferable.

Alternatively, any resin layer can be used so long as it does not solvethe dye in the recording layer when the buffer layer is made.Particularly, a polymer film which can be manufactured in vacuumevaporation or CVD method is useful.

The thickness of the buffer layer is preferably not less than 2 nm, andmore preferably not less than 5 nm. When the buffer layer is excessivelythin, prevention of the above mixing phenomenon tends to beinsufficient. The thickness of the buffer layer is preferably not largerthan 2000 nm, and more preferably not larger than 500 nm. Excessivethick buffer layer is not only necessary for prevention of the mixingbut also may cause a decrease in the optical transmission. When thelayer is made from an inorganic substance, the film deposition of thelayer takes a longer time, which causes a decrease in productivity, orthe film stress is increased. Thus, the film thickness is preferably notlarger than 200 nm. Particularly, since a film made from a metalexcessively deteriorates the optical transmittance, the film thicknessis preferably not larger than approximately 20 nm.

A protective layer may be provided in order to protect the recordinglayer or the reflective layer. The material of the protective layer isnot specifically limited but any material is available so long as itprotects the recording layer or the reflective layer from the externalforce. As an organic material of the protective layer, there are athermal plastic resin, a thermal setting resin, an electron beam settingresin, a ultraviolet ray-curable resin and the like. As an organicmaterial of the protective layer, there are silicon oxide, siliconnitride, MgF₂, SnO₂ and the like.

The protective layer can be formed by dissolving a thermal plasticresin, a thermal setting resin or the like in an appropriate solvent toprepare a coating liquid, and applying and drying the liquid. In thecase of a ultraviolet ray-curable resin, the protective layer can beformed by preparing a coating liquid of the ultraviolet ray-curableresin itself or a coating liquid obtained by dissolving the ultravioletray-curable resin in an appropriate solvent, applying the coatingliquid, irradiating UV light to set the liquid. As the ultravioletray-curable resins, there are acrylic resins such as urethane acrylate,expoxy acrylate, polyester acrylate, etc. These materials can be usedsolely or can be mixed to be used. Further, use of not only a singlelayer but also a multilayer is possible.

As the method of forming the protective layer, there are coating methodssuch as spin coating, cast and the like, sputtering, chemicalevaporation, etc. Among these, spin coating is preferable.

The film thickness of the protective layer is generally within a rangefrom 0.1 to 100 μm. In this optical recording medium, the film thicknessof the protective layer is preferably from 3 to 50 μm.

A print accepting layer, on which writing (printing) is possible withvarious printers such as ink-jet printer, thermal printer and the like,or various writing tools, may be put on a surface that is not a surfacethrough which the recording/reading beam comes in, as required.

Alternatively, it is possible to bond two optical recording media havingthis structure, with the first substrate 1 being on the outer side, toform a larger-capacity medium having four recording layers.

[1-2] Optical Recording Medium of Type 2

FIG. 2 is a sectional view of a typical optical recording medium (oftype 2) according to this embodiment.

The optical recording medium (bonded dual-layer DVD-R of a single-sidedincident type) of type 2 according to this embodiment has a firstrecording layer (first recording layer, first dye containing recordinglayer) 22 containing a dye, a semitransparent reflective layer(hereinafter referred to as a semitransparent reflective layer, firstreflective layer) 23, a transparent adhesive layer (intermediate layer)24, a buffer layer 28, a second recording layer (second recording layer,second dye containing recording layer) 25 containing a dye, a reflectivelayer (second reflective layer) 26, a second substrate (secondsubstrate) in a disk-like shape 27 in this order on a disk-like shaped,transparent (light-transmissible) first substrate (first substrate,first light-transmissible substrate) 21. The optical beam is radiatedfrom the side of the first substrate 21 to perform recording/reading. Inthis embodiment, “transparent” signifies “transparent” to the opticalbeams used for recording on or reading from the optical recording mediumlike the first embodiment.

Namely, the single-sided incident DVD-R of a bonded dual-layer type hasa first information recording body formed by stacking at least the firstdye containing recording layer 22 containing a first dye and thesemitransparent reflective layer 23 in order on the first substrate 21having guide grooves, and a second information recording body formed bystacking at least the reflective layer 26 and the second dye containingrecording layer 25 containing a second dye in order on the secondsubstrate 27 having guide grooves. This DVD-R is formed by facing theopposite sides of the substrates of the first information recording bodyand the second information recording body to each other, and bondingthem through the optically transparent adhesive layer.

Concavities and convexities are formed on the first substrate 21 and thesecond substrate 27 to form respective recording tracks. The recordingtrack may be the convex portion or the concave portion. However, it ispreferable that the recording track 31 on the first substrate 21 isformed with the convex portion with respect to the direction of theincident light beams, whereas the recording track 32 on the secondsubstrate 27 is formed with the concave portion with respect to thedirection of the incident light beams. The substrate may have concaveand convex pits as required. According to this embodiment, the convexityand the concavity are defined with respect to the direction of theincident light beams used for recording or reading unless specificallymentioned.

Next, each of the layers will be described.

The first substrate 21, the first recording layer 22, thesemitransparent reflective layer 23, the second recording layer 25 andthe reflective layer 26 of the bonded dual-layer DVD-R of thesingle-sided incident type according to this embodiment are almostsimilar in structure to the first substrate 1, the first recording layer2, the semitransparent reflective layer 3, the second recording layer 5and the reflective layer 6 of the stacked dual-layer DVD-R of thesingle-sided incident type according to the first embodiment.

The transparent adhesive layer 24 as being the intermediate layer isalmost similar in structure to the intermediate resin layer 4 of thelaminated dual-layer DVD-R of the single-sided incident type accordingto the first embodiment except that there is no need to form the groovesand pits with concavities and convexities. Incidentally, the abovegrooves and pits are formed on the second substrate 27 to be describedlater.

The buffer layer 28 as being the intermediate layer is almost similar instructure to the buffer layer described above in the first embodiment.The buffer layer may be formed only when necessary.

It is preferable that the second substrate 27 has shape stability sothat the optical recording medium has some degree of rigidity. Namely,it is preferable that the second substrate 27 has high mechanicalstability and large rigidity. When the first substrate 21 does not havesufficient shape stability, the second substrate 27 is required to haveparticularly high shape stability. In this viewpoint, the secondsubstrate 27 preferably has low moisture absorption.

It is preferable that the second substrate 27 has good molding propertybecause concavities and convexities are (recording tracks) formedthereon. The second substrate 27 is not required to be transparent.However, when the second substrate 27 is transparent, measurement of thefilm thickness of the second recording layer 25 becomes easy in themanufacturing process, which is preferable.

As such material, there can be used resins such as acrylic resins,methacrylic resins, polycarbonate resin, polyolefin resins (particularlyamorphous polyolefin), polyester resins, polystyrene resin, epoxy resinand so forth, and glass.

On the second substrate 27, concavities and convexities are spirally orconcentrically formed to form grooves and lands. Generally, such groovesand/or lands are used as recording tracks to record or read informationon or from the second recording layer 25. Since the second recordinglayer 25 is generally formed in coating, the film thickness thereof islarge at the groove portion so that the groove portion is suitable forrecording or reading. It is preferable in this optical recording mediumto assign the groove portion, that is, the concave portion to thedirection of the incident light beam, of the second substrate 27 as therecording track 32. Here, “concave portion” and “convex portion” signify“concave portion” and “convex portion” with respect to the direction ofthe incident light beam. Generally, the groove has a width of about 50to 500 nm, and has a depth of about 10 to 250 nm. When the recordingtrack is spiral, it is preferable that the track pitch is approximately0.1 to 2.0 μm. The second substrate 27 may have concave/convex pits suchas land pre-pits as required.

From the standpoint of cost, it is preferable that the second substrate27 having such concavities and convexities is made from a resin andmanufactured in injection molding with a stamper having concavities andconvexities. When a resin layer made from a radiation setting resin suchas a photo-setting resin or the like is formed on the substrate bodymade from glass or the like, concavities and convexities for recordingtracks or the like may be formed on the resin layer.

Although this invention is suited to record data in a write-once opticalrecording medium (DVD-R) having a dye containing recording layer havingthe above structure, this invention can be applied to an opticalrecording medium having another structure so long as it is an opticalrecording medium (multilayer optical recording medium) having aplurality of recording layers. For example, this invention can beapplied to a rewritable optical recording medium (for example, DVD-RW,DVD+RW, DVD-RAM or the like) having a phase-change recording layer asbeing a recording layer in which a portion in the crystalline state isused as the unrecorded state/erased state, whereas a portion in theamorphous state is used as the recorded state, or an magneto-opticalrecording medium having a magnetic recording layer as the recordinglayer, for example. This invention can be applied to not only opticalrecording media of the substrate surface incident type but also opticalrecording media of a so-called film surface incident type.

[2] Recording Apparatus for Optical Recording Medium

Next, description will be made of a recording apparatus for the opticalrecording medium according to this embodiment with reference to FIG. 3.

As shown in FIG. 3, a recording apparatus (drive, writer) 250 for thisoptical recording medium comprises a spindle motor 252 driving anoptical recording medium 251 to rotate the same, a semiconductor laser(laser light source) 253 such as a laser diode (LD) or the like, a beamsplitter 254, an objective lens 255, an optical pickup 257 including aphoto-detector 256 such as a photo diode (PD) or the like, an amplifier258 amplifying a signal detected by the optical pickup 257, a laserdriver (driving unit; for example, driving circuit) 259 driving thesemiconductor laser 253, and a control arithmetic unit 260 [including aCPU 260A and a memory (storing unit) 260B, for example].

When a record instruction (write instruction) is inputted to the controlarithmetic unit 260, the control arithmetic unit 260 outputs a controlsignal to the laser driver 259, and the laser driver 259 drives thesemiconductor laser 253. Whereby, the semiconductor laser 253 emits alaser beam (recording beam) to a desired recording layer of the opticalrecording medium 251 through the beam splitter 254, the objective lens255, etc. to record data.

In data recording, the quantity of light of the reflected light beamfrom the optical recording medium 251 is detected by the photo-detector256 through the beam splitter 254, amplified by the amplifier 258, andinputted to the control arithmetic unit 260. The control arithmetic unit260 optimizes the power of the laser beam outputted from thesemiconductor laser 253, that is, the control arithmetic unit 260performs the optimum power control (OPC).

In this embodiment, “OPC” is required to only determine the optimumvalue, thus any method is available. The optimum value determined in theOPC is referred to as an OPC recording power.

During the data recording, the control arithmetic unit 260 monitors thequantity of light of the returning light beam (reflected light;returning light of the recording beam) reflected by the opticalrecording medium 251, and controls the recording power (laser power) sothat a decrease in the quantity of reflected light beam at the time thata recording mark is formed is constant (that is, so that the asymmetryis constant).

Recording in this optical recording medium (of the type 1 and the type2) is performed by irradiating a laser beam converging to a diameter ofapproximately 0.5 to 1 μm on the recording layer from the side of thefirst substrate 1 or 21. In a portion on which the laser beam isemitted, thermal deformation of the recording layer such asdecomposition, exothermic reaction, dissolution, etc. occurs due toabsorption of the energy of the laser beam, whereby the chemicalproperties thereof are changed.

Reading of recorded information is performed by reading, with the laserbeam, a difference in reflectance between a portion in which the opticalproperties have changed and a portion in which the optical propertiesremains unchanged.

Recording or reading are performed on each of the two recording layersin the following manner. Whether the converging position of theconverged laser is on the first recording layer 2, 22 or the secondrecording layer 5, 25 can be discriminated by using a focus error signalobtained in the knife edge method, astigmatism method, Foucault methodor the like. Namely, when the objective lens for converging the laserbeam is shifted in the vertical direction, a different S-shaped curve isobtained according to whether the focus position of the laser beam is onthe first recording layer 2, 22 or on the second recording layer 5, 25.It is possible to select the first recording layer 2, 22 or the secondrecording layer 5, 25 to be recorded or read by selecting which S-shapedcurve is used for focusing servo.

In the optical recording medium of the type 1, it is preferable thatconcavities and convexities are formed on the first substrate 1 and theintermediate resin layer 4, and the convex portion of the firstsubstrate 1 and the convex portion of the intermediate resin layer 4 areused as recording tracks to perform recording or reading, as shown inFIG. 1. Since the dye recording layer is generally formed in coating,the film thereof is thick at the groove, which is thus suitable forrecording or reading. In the optical recording medium of the type 1, itis preferable that the groove, that is, the convex portion to thedirection of the incident light beam, of the first substrate 1 is usedas a recording track 11, whereas the groove, that is, the convex portionto the direction of the incident light beam, of the intermediate resinlayer 4 is used as a recording track 12.

In the optical recording medium of the type 2, it is preferable thatconcavities and convexities are formed on the first substrate 21 and thesecond substrate 27, and the convex portion of the first substrate 21and the concave portion of the second substrate 27 are used as recordingtracks to perform recording or reading, as shown in FIG. 2.Incidentally, there is a case where the polarity of the tracking servocontrol on the first recording layer 22 is opposite to that of thetracking servo control on the second recording layer 25. In the opticalrecording medium of the type 2, it is preferable that the groove, thatis, the convex portion to the direction of the incident light beam, ofthe first substrate 21 is used as a recording track 31, whereas thegroove, that is the concave portion to the direction of the incidentlight beam, of the second substrate 27 is used as a recording track 32.

As the laser beam used for this optical recording media (of the type 1and the type 2), N₂, He—Cd, Ar, He—Ne, ruby, semiconductor, dye laser,etc. are available. Among these, the semiconductor laser is preferablebecause of its light weight, compactness, facility, etc.

It is preferable that the wavelength of the used laser beam is asshorter as possible for the purpose of high-density recording.Particularly, the laser beam having a wavelength of 350 to 530 nm ispreferable. As a typical example of such laser beam, there are laserbeams having center wavelengths of 405 nm, 410 nm and 515 nm.

An example of the laser beam having a wavelength within a range from 350to 530 nm can be obtained by using a 405 nm or 410 nm blue high-powersemiconductor laser or a 515 nm bluish green high-power semiconductorlaser. Other than these, the laser beam can be obtained bywavelength-modulating, by means of a second harmonic generating element(SHG), either (a) a semiconductor laser that can continuously oscillatefundamental oscillation wavelengths of 740 to 960 nm, or (b) a solidstate laser that is excited by a semiconductor laser to be able tocontinuously oscillate fundamental oscillation wavelengths of 740 to 960nm.

As the above SHG, any piezo element lacking inversion symmetry isusable, but KDP, ADP, BNN, KN, LBO and compound semiconductors arepreferable. As practical examples of the second harmonic wave, there are430 nm which is a double of 860 nm in the case of a semiconductor laserhaving a fundamental oscillation wavelength of 860 nm, 430 nm which is adouble of 860 nm from Cr-doped LiSrAlF₆ crystal (having a fundamentaloscillation wavelength of 860 nm) in the case of a solid laser excitedby a semiconductor laser, etc.

[3] Recording Method for Optical Recording Medium

Next, description will be made of a process (recording method for theoptical recording medium) carried out by executing a predeterminedprogram by the control arithmetic unit 260 of the recording apparatus250 for the optical recording medium structured as above with referenceto FIG. 4.

When data is recorded in the above dual-layer DVD-R of the single-sidedincident type (refer to FIGS. 1 and 2), data is first recorded in thesecond recording layer 5 (25) far from the surface from which the laserbeam comes in, data is then recorded on the first recording layer 2 (22)close to the surface from which the laser beam comes in.

In the recording apparatus 250 for this optical recording medium,recording conditions such as a recording recommended power and the likewhich are recorded, in relation with layer information on each of therecording layers 2 and 5 (22 and 25), in the optical recording medium251 are read out according to an instruction from the control arithmeticunit 260 before recording on the optical recording medium 251 isperformed (for example, when the medium is loaded to the apparatus), Therecording conditions are related to the layer information on each of therecording layers 2 and 25 (22 and 25) and stored in the memory 260B.

As shown in FIG. 4, when a record instruction is inputted to therecording apparatus 250 for the optical recording medium from a computersuch as a personal computer or the like (or through an input unit suchas a button equipped to the drive thereof), the control arithmetic unit260 captures recording data (recording pulses, continuous data) sentfrom the personal computer or another equipment, for example, anddivides it into a portion to be recorded on the first recording layer 2(22) and a portion to be recorded on the second recording layer 5 (25).This function of the control arithmetic unit 260 is referred to as adata dividing unit.

Namely, the continuous data sent to be recorded on the optical recordingmedium 251 having two recording layers 2 and 5 (22 and 25) is dividedinto a first half continuous data and the latter half continuous data.Here, the first half continuous data is assigned as a portion to berecorded on the first recording layer 2 (22) close to the side fromwhich the incident light beam comes in, and the latter half continuousdata is assigned as a portion to be recorded on the second recordinglayer 5 (25) far from the side from which the incident light beam comesin.

The control arithmetic unit 260 controls the optical pickup 257 toperform the focusing servo control on the first recording layer 2 (22),thereby to perform the optimum power control on the power (laser power)of a laser beam outputted from the semiconductor laser 253 through thelaser driver 259 (step S20). Here, the control arithmetic unit 260 readsout the recording recommended power from the memory 260B on the basis ofthe layer information on the first recording layer 2 (22), and performsthe OPC on the basis of the recording recommended power read out. Thisfunction of the control arithmetic unit 260 is referred to as an optimumpower control unit.

Namely, in order to perform trial writing in the power calibration area(PCA recording power calibration area) set on the first recording layer2 (22) on which the focusing servo control has been performed, withdifferent laser powers, the control arithmetic unit 260 controls theoptical pickup 257 to adjust the laser power to the optimum power(optimum recording power, OPC recording power) to the first recordinglayer 2 (22). The control arithmetic unit 260 then stores the optimumpower (a laser current value corresponding to the optimum power) to thefirst recording layer 2 (22) obtained by performing the OPC in thememory 260B.

Next, the control arithmetic unit 260 controls the optical pickup 257 toperform the focusing servo control on the second recording layer 5 (25),thereby to perform the optimum power control (OPC) on the power (laserpower) of the laser beam outputted from the semiconductor laser 253through the laser driver 259 (step S30). Here, the control arithmeticunit 260 reads out the recording recommended power from the memory onthe basis of the layer information on the second recording layer 5 (25),and performs the OPC on the basis of the recording recommended powerread out. This function of the control arithmetic unit 260 is referredto as an optimum power control unit.

Namely, in order to perform trial writing in the PCA set on the secondrecording layer 5 (25) on which the focusing servo control has beenperformed, with different laser powers, the control arithmetic unit 260controls the optical pickup 257 to adjust the laser power to the optimumpower (optimum recording power, OPC recording power) to the secondrecording layer 5 (25). The control arithmetic unit 260 then stores theoptimum power (a laser current value corresponding to the optimum power)to the second recording layer 5 (25) obtained by performing the OPC inthe memory 260B.

Since the OPC recording powers to the respective recording layers 2 and5 (22 and 25) are set at the above steps S20 and S30, these steps arereferred to as an OPC recording power setting step.

After the OPC is performed on all the recording layers [here, the firstrecording layer 2 (22) and the second recording layer 5 (25)], data isrecorded on the recording layers 2 and 5 (22 and 25). As describedabove, the data is first recorded on the second recording layer 5 (25),then continuously recorded on the first recording layer 2 (22).

The control arithmetic unit 260 reads out the optimum power to thesecond recording layer 5 (25) stored in the memory 260B, drives thesemiconductor laser 253 through the laser driver 259, controls therecording power of the semiconductor laser 253 to the optimum power (alaser current value corresponding to the optimum power) to the secondrecording layer 5 (25), and records the latter half continuous data onthe second recording layer 5 (25) (step S40). This function of thecontrol arithmetic unit 260 is referred to as a data recording unit.

When continuously performing a recording on the first recording layer 2(22) after the recording on the second recording layer 5 (25), thecontrol arithmetic unit 260 controls the recording power of thesemiconductor laser 253 to a recording power (a laser current valuecorresponding to the recording power) at the time of a start of therecording on the first recording layer 2 (22), and records the firsthalf continuous data on the first recording layer 2 (22).

The above recording apparatus and recording method have an advantagethat the recording power to be used when data is recorded on therecording layers 2 and 5 (22 and 25) can be accurately adjusted toattain good recording. As a result, when data is continuously recordedon the recording layers 2 and 5 (22 and 25) of the optical recordingmedium 251 having a plurality of recording layers 2 and 5 (22 and 25),for example, it is possible to carry out good recording on each of therecording layers 2 and 5 (22 and 25).

In the above description, recording on the first recording layer 2 or 22is performed after recording on the second recording layer 5 or 25 isperformed. However, it is possible that the recording on the secondrecording layer 2 or 25 is performed after recording on the firstrecording layer 2 or 22 is performed, as a matter of course.

[4] Area Structure of Optical Recording Medium and Optimization ofRecording Power

When a laser beam is irradiated from the side of the first substrate 1or 21 to perform recording on a medium, the recording is first performedon the first recording layer 2 or 22, and the recording on the secondrecording layer 5 or 25 is started when a recordable area in therecording layer 2 or 22 is consumed.

Hereinafter, description will be made of the area structure and therecoding power (intensity) optimization in the case where recording isperformed from the inner peripheral side toward the outer peripheralside of the second recording layer 5 or 25 after recording is performedfrom the inner peripheral side toward the outer peripheral side of thefirst recording layer 2 or 22.

In this optical recording medium, optimization (OPC) of the recordingpower of the laser beam for each recording layer is performed, using thepower calibration area (PCA) before the recording is actually started oneach recording layer.

As shown in FIG. 5(A), a predetermined area 51, a PCA 52, a user dataarea 53 are arranged on the first recording layer 2 or 22 of thisoptical recording medium from the inner peripheral side toward the outerperipheral side of the disk.

On the second recording layer 5 or 25, a PCA 61, a predetermined area 62and a user data area 63 are arranged from the inner peripheral sidetoward the outer peripheral side of the disk.

In each of the user data area 53 and 63, a lead-in area, an informationrecording area, a lead-out area, etc. are included.

As shown in FIG. 5(B), the PCA 52 of the first recording layer 2 or 22is divided into an OPC area 52 a for performing trial writing byirradiating the laser beam, and an OPC management area 52 b forrecording the number of times the trial writing has been performed, etc.Each of the areas 52 a and 52 b consists of a plurality of partitions,and one partition (2418 bytes) is used for one OPC process in each ofthe areas 52 a and 52 b. The partitions in the OPC area 52 a are usedfrom the outer peripheral side toward the inner peripheral side, whereasthe partitions in the OPC management area 52 b are used from the innerperipheral side toward the outer peripheral side, for example.

When recording is performed on the first recording layer 2 or 22 with alaser beam, trail writing is performed by irradiating laser beams havingvarious powers on one partition in the OPC area 52 a, reading of therecords written on trails is repeated, a recording power of the laserbeam with which reading can be performed most appropriately isdetermined, and the state of use of the OPC area 52 a such as the numberof times trial writing has been performed, etc. is recorded in onepartition in the OPC management area 52 b.

The PCA 61 of the second recording layer 5 or 25 is divided into an OPCarea 61 a for performing trial writing is performed by irradiating thelaser beam, and an OPC management area 61 b for recording the number oftimes trial writing has been performed, etc. Each of the areas 61 a and61 b consists of a plurality of partitions. One partition is used forone OPC process in each of the areas 61 a and 61 b. The partitions inthe OPC area 61 a are used from the inner peripheral side toward theouter peripheral side, whereas the partitions in the OPC management area61 b are used from the outer peripheral side toward the inner peripheralside, for example.

When recording is performed on the second recording layer 5 or 25 with alaser beam, laser beams having various powers are emitted on onepartition in the OPC area 61 a to perform trial writing, reading of therecords written on trails is repeated, a recording power of the laserbeam with which reading can be performed most appropriately isdetermined, and the state of use of the OPC area 61 a such as the numberof times trail writing has been performed, etc. is recorded in onepartition in the OPC management area 61 a.

The predetermined area 62 in the second recording layer 5 or 25 is inthe state (un-recorded state) where nothing is recorded. In this opticalrecording medium, since recording on the second recording layer 5 or 25is performed after recording on the first recording layer 2 or 22 iscompleted as stated above, the second recording layer 5 or 25 is in theun-recorded state when recording is performed on the first recordinglayer 2 or 22. For this, by making the predetermined area 62 in theun-recorded state like the second recording layer 5 or 25, it ispossible to perform the OPC process on the first recording layer 2 or 22in a state closer to the practical recording conditions.

On the other hand, the predetermined area 51 in the first recording area2 or 22 is in the previously-recorded state. In this optical recordingmedium, since recording on the second recording layer 5 or 25 isperformed after recording on the first recording layer 2 or 22 iscompleted as stated above, the first recording layer is already in therecorded state when recording is performed on the second layer 5 or 25.For this, by making the predetermined area 51 in the recorded state likethe first recording layer 2 or 22, it is possible to perform the OPCprocess on the second recording layer 5 or 25 in a state closer to thepractical recording conditions.

When the applied medium is a DVD-R, it is preferable that a record inconformity with EFM+ that is a recording method for DVD-R is recorded inthe predetermined area 51. For example, the length of a mark or a spaceis preferably within a range of 3 T to 14 T when the reference clockcycle of recording is T, and a ratio of mark to space is preferably 0.9to 1.1, and more preferably 1.0 (that is, 50% duty). As this, it ispreferable that the record is recorded in the same method as therecording method generally used for data recording on the appliedmedium.

Recording in the predetermined area 51 may be performed by themanufacturer when the disk is manufactured, or may be performed by theuser with a drive when the user purchases the disk. In either case, itis only necessary that the predetermined area 51 in the first recordinglayer 2 or 22 is already recorded before the first OPC process for thesecond recording layer 5 or 25 is started.

As this optical recording medium is structured as above, the OPC processfor the first recording layer 2 or 22 is performed in the PCA 52 of thefirst recording layer 2 or 22 before recording on the first recordinglayer 2 or 22 is started. At this time, the second recording layer 5 or25 covered with the OPC area 52 a of the first recording layer 2 or 22when looked from the laser beam is in the un-recorded state.Accordingly, it is possible to perform the OPC process for the firstrecording layer 2 or 22 in a state closer to the actual recording state,whereby the optimum recording power to the first recording layer 2 or 22can be determined.

When recording on the first recording layer 2 or 22 is startedthereafter, the OPC process for the first recording layer 2 or 22 isperformed in the PCA 52 of the first recording layer 2 or 22.

When the recording on the entire first recording layer 2 or 22 iscompleted, the OPC process for the second recording layer 5 or 25 isperformed in the PCA 61 of the second recording layer 5 or 25. At thistime, the first recording layer 2 or 22 overlapping on the OPC area 61 aof the second recording layer 5 or 25 when looked from the laser beam isin the previously-recorded state. Accordingly, it is possible to performthe OPC process for the second recording layer 5 or 25 in a state closerto the actual recording state, whereby the optimum recording power tothe second recording layer 5 or 25 can be determined.

By arranging the OPC area 61 a of the second recording layer 5 or 25 notso as to be covered with the OPC area 52 a of the first recording layer2 or 22, it is possible to perform the OPC process for the secondrecording layer 5 or 25 without affected by the recording state of theOPC area 52 a of the first recording layer 2 or 22. Accordingly, it ispossible to determine the optimum recording power to the secondrecording layer 5 or 25, as well.

It is, of course, possible to beforehand record a recommended recordingpower of the laser beam in the medium, as stated above. In concrete, arecommended recording power value for each of the recording layers 2 and5 (22 and 25) is recorded with wobble of the recording track.Alternatively, it is possible to record the recommended recording powervalue with pre-pits (land pre-pits) or the like in an area (not shown)formed between the recording management area [RMA: an area formedbetween PCA and lead-in area (not shown)] of each of the recordinglayers 2 and 5 (22 and 25). The recommended recording power valuerecorded as this is referred when the OPC process is performed, wherebythe optimum recording power can be determined more quickly.

In this embodiment, the second recording layer 5 or 25 covered with theOPC area 52 a of the first recording layer 2 or 22 is in the un-recordedstate. However, it is preferable that at least a part of the secondrecording layer 5 or 25 is in the un-recorded state. The first recordinglayer 2 or 22 overlapping on the OPC area 61 a of the second recordinglayer 5 or 25 is in the previously-recorded state. However, it ispreferable that at least a part of the first recording layer 2 or 22 isin the previously-recorded state.

In this embodiment, recording on the second recording layer 5 or 25 isperformed after recording on the first recording layer 2 or 22 iscompleted. However, it is possible to perform recording on the firstrecording layer 2 or 22 after recording on the second recording layer 5or 25 is completed.

In which case, since the first recording layer 2 or 22 is in theun-recorded state when recording on the second recording layer 5 or 25is performed, it is preferable that the predetermined area 51 of thefirst recording layer 2 or 22 is in the un-recorded state. By doing so,it becomes possible to perform the OPC process for the second recordinglayer 5 or 25 in a state closer to the actual recording conditions, anddetermine the optimum power to the second recording layer 5 or 25.

Since the second recording layer 5 or 25 is in an already-recorded statewhen recording on the first recording layer 2 or 22 is performed afterrecording on the second recording layer 5 or 25 is completed, it ispreferable to make the predetermined area 62 of the second recordinglayer 5 or 25 be in the previously-recorded state. By doing so, itbecomes possible to perform the OPC process for the first recordinglayer 2 or 22 in a state closer to the actual recording conditions, anddetermine the optimum power to the first recording layer 2 or 22.

As shown in FIG. 5(A), it is preferable that the PCAs 52 and 61 arearranged at positions close to positions at which recording is startedbecause the laser beam can access there more easily. However, it isalternatively possible to arrange the PCAs 52 and 61 on the outerperipheral side of the user data areas 53 and 63, together with thepredetermined areas 51 and 62. In which case, it is preferable thatrecording on the first recording layer 2 or 22 and the second recordinglayer 5 or 25 is performed from the outer peripheral side toward theinner peripheral side in order to allow the laser beam to access thereeasily.

Still alternatively, it is possible to arrange the PCAs 52 and 61, andthe predetermined areas 51 and 62 on both the inner peripheral side andthe outer peripheral side, or arrange a plurality of PCAs and aplurality of predetermined areas in the radial direction.

[5] Another Recording Method for Optical Recording Medium

Hereinafter, description will be made of another recording method forthe optical recoding medium according to this embodiment, that is, aprocess performed by executing a predetermined program by the controlarithmetic unit 260 of the recording apparatus 250 for the opticalrecording medium structured as above, with reference to FIGS. 8, 9(A),9(B), 10(A) and 10(B).

Here, the description will be made by way of example where data isrecorded in the above dual-layer, single-sided incident type DVD-R(refer to FIGS. 1 and 2), the data is recorded on the second recordinglayer 5 (25) far from the side from which the laser beam comes in, thedata is then continuously recorded on the first recording layer 2 (22)close to the side from which the laser beam comes in. Incidentally,“continuously recording” signifies that a time interval between an endof the recording on the first recording layer 2 (22) and a start of therecording on the second recording layer 5 (25) is not considerable(within a predetermined time; for example, within 10 minutes, preferablywithin 5 minutes).

In this recording apparatus 250 for the optical recording medium,recording conditions such as recording recommended powers and the like,which are recorded in relation with the layer information on therecording layers 2 and 5 (22 and 25) in the optical recording medium251, are read out according to an instruction from the controlarithmetic unit 260 before the recording on the optical recording medium251 is performed (for example, when the medium is loaded), and therecording conditions are related with the layer information on each ofthe recording layers 2 and 5 (22 and 25) and stored in the memory 260B.

As shown in FIG. 8, when a record instruction is inputted from, forexample, a computer such as a personal computer (or through an inputunit such as a button equipped to the drive itself) to this recordingapparatus 250 for the optical recording medium, the control arithmeticunit 260 captures data to be recorded (recording pulses, continuousdata) send from, for example, the personal computer or anotherequipment, and divides the data into a portion to be recorded on thefirst recording layer 2 (22) and a portion to be recorded on the secondrecording layer 5 (25) (step A10). This function of the controlarithmetic unit 260 is referred to as a data dividing unit.

In other words, continuous data sent to be recorded on the opticalrecording medium 51 having two recording layers 2 and 5 (22 and 25) isdivided into a first half continuous data and the latter half continuousdata. Here, the first half continuous data is to be recorded on thefirst recording layer 2 (22) close to the side from which the incidentlight beam comes in, whereas the latter half continuous data is to berecorded on the second recording layer 5 (25) far from the side fromwhich the incident light beam comes in.

Next, the control arithmetic unit 260 controls the optical pickup 257 toperform the focusing servo control for the first recording layer 2 (22),and performs the optimum power control (OPC) on the power of a laserbeam outputted from the semiconductor laser 253 through the laser driver259 (step A20). Here, the control arithmetic unit 260 reads out therecording recommended power from the memory 260B on the basis of thelayer information on the first recording layer 2 (22), and performs theOPC on the basis of the recording recommended power read out. Thisfunction of the control arithmetic unit 260 is referred to as an optimumpower control unit.

In order to perform trial writing with different laser powers in thepower calibration areas (PCA, recording power calibration areas)arranged on both the inner peripheral side (in an inner peripheralportion) and the outer peripheral side (in an outer peripheral portion)of the data recording area of the first recording layer 2 (22) on whichthe focusing servo control has been performed, the control arithmeticunit 260 controls the optical pickup 257 to adjust the laser power tothe optimum power (optimum recording power, OPC recording power) suitedto the first recording layer 2 (22). The control arithmetic unit 260stores the optimum power (a laser current value corresponding to theoptimum power) to the first recording layer 2 (22) obtained byperforming the OPC in the memory 260B.

Meanwhile, the OPC is performed in each of the PCAs provided on theinner peripheral side and the outer peripheral side of the datarecording area of the first recording layer 2 (22). However, it ispossible to perform the OPC in only the PCA arranged on the innerperipheral side of the first recording layer 2 (22), or only in the PCAarranged on the outer peripheral side of the first recording layer 2(22) for example.

Next, the control arithmetic unit 260 controls the optical pickup 257 toperform the focusing servo control for the second recording layer 5(25), thereby to perform the optimum power control (OPC) on the power(laser power) of the laser beam outputted from the semiconductor laser253 through the laser driver 259 (step A30). Here, the controlarithmetic unit 260 reads out the recording recommended power from thememory 260B on the basis of the layer information on the secondrecording layer 5 (25), and performs the OPC on the basis of therecording recommended power read out. This function of the controlarithmetic unit 260 is referred to as an optimum power control unit.

In order to perform trial writing with different powers in the PCAsarranged on both the inner peripheral side and the outer peripheral sideof the data recording area of the second recording layer 5 (25) on whichthe focusing servo control has been performed, the control arithmeticunit 260 controls the optical pickup 57 to adjust the laser power to theoptimum power (optimum recording power, OPC recording power) to thesecond recording layer 5 (25). The control arithmetic unit 260 storesthe optimum power (a laser current value corresponding to the optimumpower) to the second recording layer 5 (25) obtained by performing theOPC in the memory 260B.

Meanwhile, the OPC is performed in each of the PCAs arranged on both theinner peripheral side and the outer peripheral side of the secondrecording layer 5 (25). However, this invention is not limited to this.It is alternatively possible to perform the OPC in only the PCA arrangedon the inner peripheral side of the second recording layer 5 (25), oronly in the PCA arranged on the outer peripheral side of the secondrecording layer 5 (25), for example.

Since the OPC recording powers for the respective recording layers 2 and5 (22 and 25) are set at the above steps A20 and A30, these steps arereferred to as an OPC recording power setting step.

According to this embodiment, data is recorded on the recording layers 2and 5 (22 and 25) after the OPC is performed on all the recording layers[here, the first recording layer 2 (22) and the second recording layer 5(25)]. Here, the data is first recorded on the second recording layer 5(25), then continuously recorded on the first recording layer 2 (22).

First, the control arithmetic unit 260 reads out the optimum power tothe second recording layer 5 (25) stored in the memory 260B, drives thesemiconductor laser 253 through the laser driver 259, controls therecording power of the semiconductor laser 253 to the optimum power (alaser current value corresponding to the optimum power) to the secondrecording layer 5 (25), and records the latter half continuous data onthe second recording layer 5 (25) from the outer peripheral side towardthe inner peripheral side (step A40). This function of the controlarithmetic unit 260 is referred to as a data recording unit.

According to this embodiment, a running OPC is performed during the datarecording. Namely, the control arithmetic unit 260 monitors the quantityof light of the returning light beam (reflected light; returning lightof the recording beam) reflected by the optical recording medium 251during the recording on the second recording layer 5 (25), and controlsthe recording power (laser power) to make the decrease in the quantityof reflected light beam (the quantity of a change in the quantity ofreflected light) during recording of marks constant (that is, theasymmetry is constant). Whereby, recording with the optimum asymmetrybecomes possible. This function of the control arithmetic unit 260 isreferred to as a running OPC unit.

FIG. 9(A) is a diagram showing a relationship between positions in theradial direction on the optical recording medium 251 and laser currentvalues supplied to the semiconductor laser 253 at the time that therunning OPC is performed. In FIG. 9(A), a laser current valuecorresponding to the optimum power (OPC recording power) obtained in theOPC is denoted by Iopc.

When the running OPC is performed during data recording on the opticalrecording medium 251 from the inner peripheral side toward the outerperipheral side, the laser current value supplied to the semiconductorlaser 253 tends to be gradually increased, as shown in FIG. 9(A).

If the recording is performed while the running OPC is performed, theactual laser current value supplied at positions on the side that thedata recording is ended (here, on the outer peripheral side of theoptical recording medium 251) is larger than the laser current valueIopc corresponding to the optimum power (OPC recording power) obtainedin the OPC.

FIG. 9(B) is a diagram showing a relationship between positions in theradial direction on the optical recording medium 251 and recordingpowers (laser powers) of the laser beam outputted from the semiconductorlaser 253 at the time that the running OPC is performed. In FIG. 9(B),the optimum power (OPC recording power) obtained in the OPC is denotedby Popc.

If the running OPC is performed during the data recording on the opticalrecording medium from the inner peripheral side toward the outerperipheral side, the recording power (laser power) of the laser beamoutputted from the semiconductor laser 253 tends to be graduallyincreased, as shown in FIG. 9(B).

If recording is performed while the running OPC is performed, the actualrecording power at positions on the side that the data recording isended (here, the outer peripheral side of the optical recoding medium251) is larger than the optimum power (OPC recording power) Popcobtained in the OPC. Incidentally, since the feedback control isperformed on the basis of the quantity of the reflected light in therunning OPC, the asymmetry is constant when the recording is performedwhile the running OPC is performed.

Since the actual recording power (actual laser current value) changesrelative to the optimum power (OPC recording power) Popc (laser currentvalue Iopc corresponding thereto) obtained in the OPC when the runningOPC is performed, the recording power (laser current value) for thefirst recording layer 2(22) is set in a manner to be described later tobe used when the recording is started.

The running OPC is not always necessary although the running OPC isperformed here.

FIG. 10(A) is a diagram showing a relationship between positions in theradial direction on the optical recording medium 251 and laser currentvalues supplied to the semiconductor laser 253 at the time that therunning OPC is not performed. In FIG. 10(A), the laser current valuecorresponding to the optimum power (OPC recording power) obtained in theOPC is denoted by Iopc.

If the running OPC is not performed during data recording on the opticalrecording medium from the inner peripheral side toward the outerperipheral side, the laser current value supplied to the semiconductorlaser 253 is constant, as shown in FIG. 10(A).

For this, the actual laser current value supplied at positions on theside that the data recording is ended (here, the outer peripheral sideof the optical recording medium 251) is equal to the laser current valueIopc corresponding to the optimum power (OPC recording power) obtainedin the OPC.

FIG. 10(B) is a diagram showing a relationship between positions in theradial direction on the optical recording medium 251 and recordingpowers (laser powers) of the laser beam outputted from the semiconductorlaser 253 at the time that the running OPC is not performed. In FIG.10(B), the optimum power (OPC recording power) obtained in the OPC isdenoted by Popc.

If the running OPC is not performed during data recording on the opticalrecording medium 251 from the inner peripheral side toward the outerperipheral side, the recording power (laser power) of the laser beamoutputted from the semiconductor laser 253 tends to be graduallydecreased, as shown in FIG. 10(B).

For this, the actual recording power at positions on the side that thedata recording is ended is smaller than the optimum power (OPC recordingpower) Popc obtained in the OPC. Incidentally, if the recording isperformed without the running OPC, the asymmetry gradually decreases.

If the running OPC is not performed, the actual laser current valueremains unchanged relative to the laser current value Iopc correspondingto the optimum power (OPC recording power) Popc obtained in the OPC, butthe actual recording power changes relative to the optimum power (OPCrecording power) Popc obtained in the OPC, as above. For this reason,the recording power (laser current value) is set in a manner to bedescribed later to be used when the recording on the first recordinglayer 2 (22) is started.

When the recording of the data on the second recording layer 5 (25) iscompleted, the control arithmetic unit 260 sets the recording power(here, a laser current value corresponding to the recording power) to beused when the recording on the first recording layer 2 (22) is startedin the following manner (steps A50 and A60; recording power setting stepat the starting of the recording). Incidentally, this function of thecontrol arithmetic unit 260 B is referred to as starting point recordingpower setting unit.

In concrete, when the recording in the second recording layer 5 (25) iscompleted, the control arithmetic unit 260 determines how much theactual recording power changes relative to the optimum power to thesecond recording layer 5 (25) obtained beforehand at step A30 (stepA50).

In this embodiment, the control arithmetic unit 260 stores the recordingpower (laser current value corresponding to the recording power) whichis set to record the last data on the second recording layer 5 (25)(data recorded at the last address of the recorded data recorded on thesecond recording layer) in the memory 260B.

When the recording on the second recording layer 5 (25) is completed,the control arithmetic unit 260 reads out the optimum power to thesecond recording layer 5 (25) (OPC recording power; laser current valuecorresponding to the optimum power) which is stored in the memory 260Band the recording power (laser current value corresponding to therecording power) set to record the last data on the second recordinglayer 5 (25), and obtains a difference between the recording power usedto record the last data on the second recording layer 5 (25) and thepredetermined optimum power to the second recording layer 5 (25), andcalculates the quantity of a change in the actual recording powerrelative to the optimum power to the second recording layer 5 (25) (stepA50). This function of the control arithmetic unit 260 is referred to asa recording power changing quantity calculating unit.

According to this embodiment, the control arithmetic unit 260 subtractsthe previously-determined optimum power (laser current valuecorresponding to the optimum power) to the second recording layer 5 (25)from the recording power (laser current value corresponding to therecording power) used to record the last data on the second recordinglayer 5 (25), and calculates the quantity of a change in the actualrecording power relative to the optimum power to the second recordinglayer 5 (25) in order to perform the recording while the running OPC isperformed.

If the running OPC is not performed, a temperature sensor or aphotodiode for monitoring may be provided to estimate (a change in) theactual recording power on the basis of the temperature of thesemiconductor laser 253 or the quantity of the emitted light from thesemiconductor laser 253, a difference between the estimated actualrecording power and the previously-determined optimum power to thesecond recording layer 5 (25) may be obtained, and the quantity of achange in the actual recording power relative to the optimum power tothe second recording layer 5 (25) may be calculated.

Here, the OPC is performed in each of the PCAs arranged on the innerperipheral side and the outer peripheral side of the data recording areaof the second recording layer 5 (25), and the optimum powers obtained inthe OPC are stored in the memory 260B, as stated above. For this, thecontrol arithmetic unit 260 reads out both of the optimum recordingpowers (laser current values corresponding to the respective optimumpowers), determines the optimum power (laser current value correspondingto the optimum power) determined by an OPC performed in a PCA which isnear a portion on which the last data of the second recording layer 5(25) is recorded, on the basis of a position in the radial directionwhere the last data of the second recording layer 5 (25) is recorded andpositions in the radial direction of the PCAs on the inner peripheralside and the outer peripheral side of the second recording layer 5 (25),and uses the determined optimum power as the optimum power (lasercurrent value corresponding to the optimum power) to the secondrecording layer 5 (25).

However, the method for determining the optimum power to the secondrecording layer 5 (25) is not limited to the above example. For example,it is possible to interpolate values between a position in the radialdirection of a PCA on the inner peripheral side of the second recordinglayer 5 (25) and the optimum power (laser current value corresponding tothe optimum power) obtained in the OPC performed in this PCA, and aposition in the radial direction of a PCA on the outer peripheral sideof the second recording layer 5 (25) and the optimum power (lasercurrent value corresponding to the optimum power) obtained in OPCperformed in this PCA, determine the optimum power to a portion (aposition in the radial direction) on which the last data of the secondrecording layer 5 (25) is recorded, and use it as the optimum power tothe second recording layer 5 (25).

Alternatively, without taking into consideration a position in theradial direction on the second recording layer 5 (25), it is possible todetermine an average value of the optimum powers determined in the OPCperformed in the PCAs on the inner peripheral side and the outerperipheral side of the second recording layer 5 (25), and use it as theoptimum power to the second recording layer 5 (25), for example.

In this embodiment, the recording power is set in the running OPC on thebasis of the quantity of the reflected light beam when data is recordedon the second recording layer 5 (25). Accordingly, this means that theactual recording power (a change therein) is estimated on the basis ofthe quantity of reflected light from the optical recording medium at thetime that the last data is recorded on the second recording layer 5(25). Incidentally, this function of the control arithmetic unit 260 isreferred to as a recording power estimating unit.

When recording is performed while the running OPC is performed as donein this embodiment, the laser current value is set in the feedbackcontrol performed as the running OPC on the basis of the quantity ofreflected light, as shown in FIG. 9(A) [because it varies with a changein the actual recording power [refer to FIG. 9(B)]]. This means that (achange in) the actual recording power is estimated on the basis of thelaser current value set in the running OPC [that is, a laser currentvalue set to record the last data on the second recording layer 5 (25)].This function of the control arithmetic unit 260 is referred to as arecording power estimating unit.

In other words, obtaining a difference between an actual laser currentvalue set to record the last data on the second recording layer 5 (25)in the feedback control performed as the running OPC on the basis of thequantity of reflected light performed as the running OPC and a lasercurrent value corresponding to the optimum power (OPC recording power)obtained in the OPC on the second recording layer 5 (25) and calculatingthe quantity of a change in the actual laser current value relative tothe laser current value corresponding to the optimum power to the secondrecording layer 5 (25) is equivalent to obtaining a difference between arecording power used to record the last data of the second recordinglayer 5 (25) and the previously-determined optimum power to the secondrecording layer 5 (25) and calculating the quantity of a change in theactual recording power relative to the optimum power to the secondrecording layer 5 (25).

Here, the quantity of a change in the actual recording power isdetermined in the feedback control performed as the running OPC on thebasis of the quantity of reflected light. Alternatively, it is possibleto prepare a relationship between the quantities of reflected light andthe recording powers as a table, and determine the quantity of a changein the actual recording power using the table.

Next, the control arithmetic unit 260 corrects the previously-determinedoptimum power to the first recording layer 2 (22) on the basis of achange in the actual recording power relative to the optimum power tothe second recording layer 5 (25), and sets a recording power to be usedwhen the recording on the first recording layer 2 (22) is started (stepA60). This function of the control arithmetic unit 260 is referred to asan optimum power correcting unit.

Namely, the control arithmetic unit 260 reads out the optimum power (OPCrecording power; a laser current value corresponding to the optimumpower) to the first recording layer 2 (22) stored in the memory 260B,and adds the quantity of a change in the actual recording power relativeto the optimum power to the second recording layer 5 (25), and sets arecording power to be used when the recording on the first recordinglayer 2 (22) is started.

When the recording on the first recording layer 2 (22) is continuouslyperformed after the recording on the second recording layer 5 (25), thecontrol arithmetic unit 260 controls the recording power of thesemiconductor laser 253 to the recording power (a laser current valuecorresponding to the recording power) to be used when the recording onthe first recording layer 2 (22) is started without performing the OPCfor the first recording layer 2 (22), and records a first halfcontinuous data on the first recording layer 2 (22) from the outerperipheral side toward the inner peripheral side (step A70). Accordingto this embodiment, the running OPC is performed when the recording onthe first recording layer 2 (22) is performed as well as the recordingon the second recording layer 5 (25). This function of the controlarithmetic unit 260 is referred to as a data recording unit.

In the above embodiment, the OPC is performed on all the layers beforethe recording on the optical recording medium 251, data is then recordedon each of the recording layers. However, it is not always necessary tobeforehand perform the OPC on all recording layers. When continuousrecording is performed on at least two recording layers, the OPC shouldnot be performed before a start of recording on one recording layerafter recording on the other recording layer is completed.

In the above embodiment where the running OPC is performed duringrecording, the control arithmetic unit 260 obtains a difference betweena recording power set to record the last data of the second recordinglayer 5 (25) and the optimum power to the second recording layer 5 (25)when the recording on the first recording layer 2 (22) is started, andcalculates the quantity of a change in the actual recording powerrelative to the optimum power to the second recording layer 5 (25),thereby estimating a change in the actual recording power on the basisof the quantity of reflected light from the optical recording medium 251obtained when the recording on the second recording layer 5 (25) isended. However, this recording method is not limited to the above.

For example, the control arithmetic unit 260 may estimate a change inthe actual recording power on the basis of the temperature of thesemiconductor laser (laser light source) 253 obtained when the recordingon the second recording layer 5 (25) is completed. This method can beapplied to not only a case where the recording is performed while therunning OPC is performed, but also a case where the recording isperformed without the running OPC. Incidentally, this function of thecontrol arithmetic unit 260 is referred to as a recording powerestimating unit.

In which case, it is preferable that a temperature sensor 261 fordetecting the temperature of the semiconductor laser 253 is provided asdenoted by a chain double-dashed line in FIG. 3, for example, and thecontrol arithmetic unit 260 monitors the temperature of thesemiconductor laser 253 when recording on the second recording layer 5(25) is performed, and estimates a change in the actual recording poweron the basis of the temperature of the semiconductor laser 253 obtainedafter the recording on the second recording layer 5 (25) is completed(for example, when the last data is recorded).

For example, a table representing a relationship between thetemperatures of the semiconductor laser 253 and the recording powers [arelationship of the quantity of a change in the laser power relative toa change in temperature of the semiconductor laser 253], or a tablerepresenting a relationship between the temperatures of thesemiconductor laser 253 and the wavelengths of the outputted laser beam[a relationship of the quantity of a change in the absorbed quantity ofthe laser beam by a dye contained in the dye containing recording layer5 (25) relative to a change in temperature of the semiconductor laser253] may be beforehand prepared, and a change in the actual recordingpower may be estimated using these tables on the basis of thetemperature of the semiconductor laser 253 obtained after the recordingon the second recording layer 5 (25) is completed.

Alternatively, the control arithmetic unit 260 may estimate a change inthe actual recording power on the basis of the quantity of an emittedlight beam of the semiconductor laser (laser light source) 253 at thetime that the last data is recorded on the second recording layer 5 (25)(at the time of completion of the recording), for example. This methodcan be applied to not only the case where recording is performed whilethe running OPC is performed but also the case where recording isperformed without the running OPC. Incidentally, this function of thecontrol arithmetic unit 260 is referred to as a recording powerestimating unit.

In which case, a photodiode for monitoring (optical detector formonitoring) 262 detecting the quantity of a light beam emitted from thesemiconductor laser 253 may be provided as denoted by a chaindouble-dashed line in FIG. 3, for example, and the control arithmeticunit 260 may monitor the quantity of the emitted light beam from thesemiconductor laser 253 at the time of recording on the second recordinglayer 5 (25), and estimate a change in the actual recoding power on thebasis of the quantity of the emitted light beam from the semiconductorlaser 253 at the time that the recording on the second recording layer 5(25) is completed.

For example, a table representing a relationship between the quantitiesof the emitted light beam from the semiconductor laser 253 and therecording powers may be beforehand prepared, and a change in the actualrecording power may be estimated on the basis of the temperature of thesemiconductor laser 253 at the time of completion of the recording onthe second recording layer 5 (25), using the table.

Further, the control arithmetic unit 260 may estimate a change in theactual recording power on the basis of a time period of laserirradiation until the last data is recorded (until the end of therecording) on the second recording layer 5 (25). This method can beapplied not only to a case where recording is performed while therunning OPC is performed but also a case where recording is performedwithout the running OPC. Incidentally, this function of the controlarithmetic unit 260 is referred to as a recording power estimating unit.

In which case, the control arithmetic unit 260 monitors the time periodof laser irradiation when recording on the second recording layer 5 (25)is performed, and estimates a change in the actual recording power onthe basis of the time period of the laser irradiation until the end ofthe recording on the second recording layer 5 (25).

For example, a table representing a relationship between the timeperiods of laser irradiation and the recording powers is beforehandprepared, and a change in the actual recording power is estimated on thebasis of the time period of laser irradiation, using the table.

Further, it is possible to combine these methods and use them. Forexample, the control arithmetic unit 260 may estimate a change in theactual recording power on the basis of the quantity of the emitted lightbeam from the semiconductor laser (laser light source) 253 obtained whenthe recording on the second recording layer 5 (25) is completed, and thetemperature of the semiconductor laser (laser light source) 53 obtainedafter the recording on the second recording layer 5 (25) is completed.This method can be applied to not only a case where recording isperformed while the running OPC is performed but also a case whererecording is performed without the running OPC. Incidentally, thisfunction of the control arithmetic unit 260 is referred to as arecording power estimating unit.

In the above embodiment, the description has been made by way of examplewhere data is continuously recorded on the optical recording medium 251having the two recording layers 2 and 5 (22 and 25). Accordingly, thedata is continuously recorded on the neighboring two recording layers.However, when data is continuously recorded on an optical recordingmedium having three or more recording layers, for example, the recordingis not necessarily performed continuously on neighboring recordinglayers.

[B] Second Embodiment

According to this embodiment, the area structure of the opticalrecording medium and the optimization of the recording power differ fromthose of the first embodiment.

Hereinafter, description will be made of the area structure and theoptimization of the recording power according to this embodiment.

In this optical recording medium (of the type 1 and the type 2),recording is performed on the first recording layer 2 or 22 from theinner peripheral side toward the outer peripheral side, after that, therecording is performed on the second recording layer 5 or 25 from theouter peripheral side toward the inner peripheral side, as shown in FIG.6(A).

In this optical recording medium, optimization (OPC) of the recordingpower of the laser beam is performed for each of the recording layersusing PCAs before actual recording is started on each of the recordinglayers, as well.

As shown in FIG. 6(A), a PCA 71, a user data area 73 and a predeterminedarea 75 are arranged in order on the first recording layer 2 or 22 ofthis optical recording medium from the inner peripheral side toward theouter peripheral side of the disk.

On the second recording layer 5 or 25, a predetermined area 81, a userdata area 83 and a PCA 85 are arranged in order from the innerperipheral side toward the outer peripheral side of the disk.

Each of the user data areas 73 and 83 includes a lead-in area, aninformation recording area, a lead-out area, etc.

As shown in FIG. 6(B), the PCA 71 of the first recording layer 2 or 22is divided into an OPC area 71 a for trial writing by irradiating thelaser beam, and an OPC management area 71 b for recording the number oftime the trial writing has been performed. Each of the areas 71 a and 71b consists of a plurality of partitions, and one partition (2418 bytes)is used in each of the regions 71 a and 72 b for one OPC process.Incidentally, the partitions in the OPC area 71 a are used from theouter peripheral side toward the inner peripheral side, whereas thepartitions in the OPC management area 71 b are used from the innerperipheral side toward the outer peripheral side, for example.

When recording on the first recording layer 2 or 22 is performed with alaser beam, trial writing is performed by irradiating laser beams havingvarious powers on one partition in the OPC area 71 a, the recordswritten on trials and reading-out are repetitively done, a recordingpower of the laser beam at which the data can be read most appropriatelyis determined, and a state of use of the OPC area 71 a such as thenumber of times the trial writing has been performed, etc. is written inone partition in the OPC management area 71 b.

As shown in FIG. 6(C), the PCA 85 of the second recording layer 5 or 25is divided into an OPC area 85 a for performing trial writing byirradiating the laser beam, and an OPC management area 85 b forrecording the number of times the trial writing has been performed. Eachof the areas 85 a and 85 b consists of a plurality of partitions, andone partition is used in each of the regions 85 a and 85 b for one OPCprocess. Incidentally, the partitions in the OPC area 85 a are used fromthe inner peripheral side toward the outer peripheral side, whereas thepartitions in the OPC management area 85 b are used from the outerperipheral side toward the inner peripheral side, for example.

When recording on the second recording layer 5 or 25 is performed with alaser beam, trial writing is performed by irradiating laser beams havingvarious powers on one partition in the OPC area 85 a to write on trials,the records written on trials are repetitively read, a recording powerof the laser beam at which the data can be read most appropriately isdetermined, and a state of use of the OPC area 85 a such as the numberof times the trial writing has been performed, etc. is written in onepartition in the OPC management area 85 b.

Meanwhile, the predetermined area 81 of the second recording layer 5 or25 is in a state where nothing is recorded. The second recording layer 5or 25 is in the un-recorded state when recording on the first recordinglayer 2 or 22 is performed because recording on the second recordinglayer 5 or 25 is performed after recording on the first recording layer2 or 22 is completed in this optical recording medium, as stated above.For this, by making the predetermined area 81 in the un-recorded statelike the second recording layer 5 or 25, it is possible to perform theOPC process on the first recording layer 2 or 22 in a state closer tothe actual recording state.

On the other hand, the predetermined area 75 of the first recordinglayer 2 or 22 is in the previously-recorded state. In this opticalrecording medium, since the recording on the second recording layer 5 or25 is performed after recording on the first recording layer 2 or 22 iscompleted, the first recording layer is already in the recorded statewhen recording on the second recording layer 5 or 25 is performed. Forthis, by making the predetermined area 75 in the recorded state, it ispossible to perform the OPC process on the second recording layer in astate closer to the actual recording state.

When the applied medium is a DVD-R, it is preferable that recording inconformity with EFM+, which is a recording method for DVD-R, isperformed in the predetermined area 75. For example, the length of amark or space is within a range of 3 T to 14 T when the reference clockcycle for recording is T, and a ratio of mark to space is 0.9 to 1.1,more preferably 1.0 (that is, 50% duty). As this, it is preferable thatdata is recorded in the same method as the recording method generallyused for data recording in the applied medium.

Recording on the predetermined area 75 may be performed by themanufacturer when the disk is manufactured, or by the user with a driveafter the user purchases the disk. In either case, it is only necessarythat the predetermined area 75 is in the previously-recorded statebefore the first OPC process is started on the second recording layer 5or 25.

In this optical recording medium having the above structure, the OPCprocess for the first recording layer 2 or 22 is performed in the PCA 71of the first recording layer 2 or 22 before recording on the firstrecording layer 2 or 22 is started. Since the second recording layer 5or 25 covered with the OPC area 71 a of the first recording layer 2 or22 when looked from the laser beam is in the un-recorded state at thistime, it is possible to perform the OPC process for the first recordinglayer 2 or 22 in a state closer to the actual recording state, anddetermine the optimum recording power to the first recording layer 2 or22.

When recording on the first recording layer is started thereafter, theOPC process for the first recording layer 2 or 22 is performed, usingthe PCA 71 of the first recoding layer 2 or 22.

When recording on the entire area of the first recording layer 2 or 22is completed, the OPC process for the second recording layer 5 or 25 isperformed, using the PCA 85 of the second recording layer 5 or 25. Sincethe first recording layer 2 or 22 overlapping when looked from the laserbeam on the OPC area 85 a of the second recording layer 2 or 25 is inthe previously-recorded state, it is possible to perform the OPC processon the second recording layer 5 or 25 in a state closer to the actualrecording state, and determine the optimum recording power to the secondrecording layer 5 or 25.

By arranging the OPC area 85 a of the second recording layer 5 or 25 soas not to be overlapped on the OPC area 71 a of the first recordinglayer 2 or 22, it is possible to perform the OPC process for the secondrecording layer 5 or 25 without affected by the recording state of theOPC area 71 a of the first recording layer 2 or 22, thereby to determinethe optimum recording power to the second recording layer 5 or 25.

Like the first embodiment, a recommended recording power value of thelaser beam may be beforehand recorded in the medium. By doing so, itbecomes possible to determine the optimum recording power more quicklyby referring to the recommended recording power when the OPC process isexecuted.

In this embodiment, the second recording layer 5 or 25 covered with theOPC area 71 a of the first recording layer 2 or 22 is in the un-recordedstate. However, it is preferable that at least a part of the secondrecording layer 5 or 25 is in the un-recorded state. The first recordinglayer 2 or 22 overlapping on the OPC area 85 a of the second recordinglayer 5 or 25 is in the previously-recorded state. However, it ispreferable that at least a part of the first recording layer 2 or 22 isin the previously-recorded state.

As shown in FIG. 6(A), it is preferable that each of the PCA 71 and 85is arranged at a position close to a position at which recording isstarted because of the accessibility of the laser beam.

[C] Third Embodiment

According to this embodiment, the area structure of the opticalrecording medium and the recording power optimization differ from thoseaccording to the first embodiment.

Hereinafter, description will be made of the area structure of theoptical recording medium and the recording power optimization accordingto this embodiment.

As shown in FIG. 7(A), in this optical recording medium (Type 1 and Type2), recording is performed on the second recording layer 5 or 25 fromthe inner peripheral side toward the outer peripheral side, after that,recoding is performed on the first recording layer 2 or 22 from theouter peripheral side toward the inner peripheral side thereof.

In this optical recording medium, before recording is actually performedon each of the recording layers, optimization of the recording power ofthe laser beam (OPC) for each of the recording layer is performed, usingPCAs.

As shown in FIG. 7(A), a PCA 101, a user data area 103 and apredetermined area 105 are arranged in order on the second recordinglayer 5 or 25 of this optical recording medium from the inner peripheralside toward the outer peripheral side of the disk.

On the first recording layer 2 or 22, a predetermined area 91, a userdata area 93 and a PCA 95 are arranged in order from the innerperipheral side toward the outer peripheral side of the disk.

Each of the user data areas 93 and 103 includes a lead-in area, aninformation recording area, a lead-out area, etc.

As shown in FIG. 7(B), the PCA 101 of the second recording layer 5 or 25is divided into an OPC area 101 a for performing trial writing byirradiating laser beams, and an OPC management area 101 b for storingthe number of times the trial writing has been performed, etc. Each ofthe areas 101 a and 101 b consists of a plurality of partitions, and onepartition (2418 byte) is used for one OPC process in each of the areas101 a and 101 b. Incidentally, the partitions in the OPC area 101 a areused from the outer peripheral side toward the inner peripheral side,whereas the partitions in the OPC management area 101 b are used fromthe inner peripheral side toward the outer peripheral side, for example.

When recording on the second recording layer 5 or 25 is performed withthe laser beam, trial writing is performed by radiating laser beamshaving various powers on one partition in the OPC area 101 a, therecords written on trials are repetitively read, a recording power ofthe laser beam that can read most appropriately is determined, and thestate of use of the OPC area 101 a such as the number of times the trialwriting has been performed, etc. is recorded in one partition in the OPCmanagement area 101 b.

As shown in FIG. 7(C), the PCA 95 of the first recording layer 2 or 22is divided into an OPC area 95 a for performing trial writing byirradiating laser beams, and an OPC management area 95 b for storing thenumber of times the trial writing has been performed, etc. Each of theareas 95 a and 95 b consists of a plurality of partitions, and onepartition (2418 byte) is used for one OPC process in each of the areas95 a and 95 b. Incidentally, the partitions in the OPC area 95 a areused from the inner peripheral side toward the outer peripheral side,whereas the partitions in the OPC management area 95 b used from theouter peripheral side toward the inner peripheral side, for example.

When recording on the first recording layer 2 or 22 is performed withthe laser beam, trial writing is performed by irradiating laser beamshaving various powers on one partition in the OPC area 95 a, the recordswritten on trials and reading-out are repetitively done, a recordingpower of the laser beam that can read most appropriately is determined,and the state of use of the OPC area 95 a such as the number of timesthe trial writing has been performed, etc. is recorded in one partitionin the OPC management area 95 b.

Meanwhile, the predetermined area 91 of the first recording layer 2 or22 is in a state where nothing is recorded (un-recorded state). Sincerecording on the first recording layer 2 or 22 is performed afterrecording on the second recording layer 5 or 25 is completed in thisoptical recording medium, as stated above, the first recoding layer 2 or22 is in the un-recorded state when recording is performed on the secondrecording layer 5 or 25. By making the predetermined area 91 in theun-recorded state like the first recording layer 2 or 22, it is possibleto perform the OPC process for the second recording layer 5 or 25 in astate closer to the actual recording state.

On the other hand, the predetermined area 105 of the second recordinglayer 5 or 25 is in the previously-recorded state. Since recording onthe first recording layer 2 or 22 is performed after recording on thesecond recording layer 5 or 25 is completed in this optical recordingmedium, as stated above, the second recoding layer 5 or 25 is already inthe recorded state when recording is performed on the first recordinglayer 2 or 22. By making the predetermined area 105 in the recordedstate like the second recording layer 5 or 25, it is possible to performthe OPC process for the first recording layer 2 or 22 in a state closerto the actual recording state.

When the applied medium is a DVD-R, it is preferable that recording inconformity with EFM+, which is a recording method for DVD-R, isperformed in the predetermined area 105. For example, it is preferablethat the length of a mark or space is within a range of 3 T to 14 T whenthe reference clock cycle for recording is T, and the ratio of mark tospace is 0.9 to 1.1, more preferably 1.0 (that is, 50% duty). As this,it is preferable that data is recorded in the same method as therecording method generally used for data recording in the appliedmedium.

Recording in the predetermined area 105 may be performed by themanufacturer when the disk is manufactured, or by the user with a driveafter the user purchases the disk. In either case, it is only necessarythat the predetermined area 105 of the second recording layer 5 or 25 isin the previously-recorded state before the first OPC process for thefirst recording layer 2 or 22 is started.

In this optical recording medium having the above structure, the OPCprocess for the second recording layer 5 or 25 is performed using thePCA 101 of the second recording layer 5 or 25 before recording on thesecond recording layer 5 or 25 is started. Since the first recordinglayer 2 or 22 overlapping when looked from the laser beam on the OPCarea 101 a of the second recording layer 5 or 25 is in the un-recordedstate at this time, it is possible to perform the OPC process for thesecond recording layer 5 or 25 in a state closer to the actual recordingstate, and determine the optimum recording power to the second recordinglayer 5 or 25.

When recording on the second recording layer 5 or 25 is startedthereafter, the OPC process for the second recording layer 5 or 25 isperformed, using the PCA 101 of the second recoding layer 5 or 25.

When recording on the entire area of the second recording layer 5 or 25is completed, the OPC process for the first recording layer 2 or 22 isperformed, using the PCA 95 of the first recording layer 2 or 22. Sincethe second recording layer 5 or 25 overlapped on the OPC area 95 a ofthe first recording layer 2 or 22 when looked from the laser beam is inthe previously-recorded state, it is possible to perform the OPC processfor the first recording layer 2 or 22 in a state closer to the actualrecording state, and determine the optimum recording power to the firstrecording layer 2 or 22.

By arranging the OPC area 95 a of the first recording layer 2 or 22 soas not to overlap on the OPC area 101 a of the second recording layer 5or 25, it is possible to perform the OPC process for the secondrecording layer 5 or 25 without affected by the recording state of theOPC area 95 a of the first recording layer 2 or 22, and determine theoptimum recording power to the second recording layer 5 or 25.

Like the first embodiment, a recommended recoding power of the laserbeam may be beforehand recorded. By doing so, it becomes possible todetermine the optimum recording power more quickly by referring to therecommended recording power when the OPC process is executed.

As shown in FIG. 7(A), it is preferable that each of the PCAs 95 an 101is arranged in a position close to where recording is started because ofthe accessibility of the laser beam.

[D] Others

Having described the embodiments of the present invention, it is to beunderstood that the present invention is not limited to be aboveembodiments, but may be modified in various ways without departing fromthe scope of the present invention.

For example, this invention can be applied to an optical recordingmedium having three or more recording layers, on which recording orreading are performed with a laser beam from one side. In which case,the PCA is arranged in each of the recording layers. In such opticalrecording medium, when the OPC process is performed on a certainrecording layer (excepting the first recording layer) X_(n), the PCA ofthe recording layer X_(n) preferably has an area not overlapped on thePCA of a recording layer X_(n-1) positioning in front thereof whenlooked from the laser beam. Further, it is preferable that a part of therecording layer X_(n-1) overlapping on the PCA of the recording layerX_(n) looked from the laser beam is in the previously-recorded state.

In the above embodiment, a dye recording medium having a dye recordinglayer has been described. However, this invention can be applied to amedium of the phase-change type. In the case of a phase-change medium,the first recording layer is comprised of the first protective layer, aninformation recording layer and the second protective layer, whereas thesecond recording layer is comprised of the first protective layer, aninformation recording layer and the second protective layer, althoughnot shown.

As the material of this information recording layer, it is preferable touse a material whose optical constant (refractive index n, extinctioncoefficient k) is changed by irradiating a laser beam. As such material,there are, chalcogenides based on Te or Se such as alloys containingGe—Sb—Te, Ge—Te, Pd—Ge—Sb—Te, In—Sb—Te, Sb—Te, Ag—In—Sb—Te, Ge—Sb—Bi—Te,Ge—Sb—Se—Te, Ge—Sn—Te, Ge—Sn—Te—Au, Ge—Sb—Te—Cr, In—Se, In—Se—Co or thelike as the main component, and alloys to which nitrogen, oxygen, etc.are appropriately added to the former alloys, for example.

As the material of the first protective layer and the second protectivelayer, it is preferable to use a material which is physically andchemically stable, has higher melting point than that of the informationrecording layer and high softening temperature, and is not mutuallysoluble with the material of the information recording layer in order tosuppress an increase in noise due to thermal damage of the protectivesubstrate, the information recording layer and the like at the time ofirradiation of the laser beam, adjust the reflectance and absorptivityto the laser beam, the phase of the reflected light, etc. As suchmaterial, there are oxides of Y, Ce, Ti, Zr, Nb, Ta, Co, Zn, Al, Si, Ge,Sn, Pb, Sb, Bi, Te or the like, nitrides of Ti, Zr, Nb, Ta, Cr, Mo, W,B, Al, Ga, In, Si, Ge, Sn, Pb or the like, carbides of Ti, Zr, Nb, Ta,Cr, Mo, W, Si or the like, sulfides of Zn, Cd or the like, selenides,tellurides, fluorides of Mg, Ca or the like, simple substances of C, Si,Ge and the like, dielectrics made from mixtures of these, and materialstreated in the same way as the dielectrics, for example. For the firstprotective layer and the second protective layer, different materialsmay be used as needed, or the same material may be used.

In the case of a rewritable optical recording medium, the OPC processcan be repeated in the same partition since it is possible to rewritesignals in the recording layer. Accordingly, the PCA of the rewritableoptical recording medium is comprised of only the OPC area, thus the OPCmanagement area for recording the number of times trial writing has beenperformed, etc. is unnecessary.

In the rewritable optical recording medium, a partition for performingthe OPC is arbitrarily selected, and the OPC process is performed aftera laser beam for erasing the power beforehand recorded in the selectedpartition of the medium is emitted and the signals are erased. Sincerecords of signals can be erased in the rewritable recording medium, theorder of the recording is not constant in such a way that the secondrecording layer is recorded after the first recording layer is recorded,thus the order of the recording differs according to the state of use.In the case of the rewritable optical recording medium, it is preferablethat the predetermined areas of the first recording layer and the secondrecording layer are in the recorded state because the OPC process can beperformed in a state closer to the actual recording state. However, thepresent invention is more effective when the present invention isapplied to a write-once medium in which data is written in one recordinglayer, after that, the data is started to be recorded in anotherrecording layer.

This application is based on Japanese Patent Application Number2002-370934 filed on Dec. 20, 2002, Japanese Patent Application No.2003-202321 filed on Jul. 28, 2003 and Japanese Patent Application No.2003-098320 filed on Apr. 1, 2003, the whole contents of which arehereby incorporated by reference.

1. An optical recording medium comprising: an optical-transmissiblefirst substrate; a first recording layer disposed on said firstsubstrate, on which information can be recorded by irradiating a laserbeam from the first substrate's side; a second recording layer disposedon said first recording layer, on which information can be recorded byirradiating said laser beam; and each of said first recording layer andsaid second recording layer including power calibration areas tooptimizing intensity of said laser beam; wherein recording ofinformation on said first recording layer and recording of informationin said second recording layer are performed forward oppositedirections.
 2. The optical recording medium according to claim 1,wherein recording of information on said first recording layer isperformed before recording of information on said second recordinglayer.
 3. The optical recording medium according to claim 2, wherein apart of said first recording layer overlapping on said power calibrationarea of said second recording layer is in a previously-recorded state.4. The optical recording medium according to claim 1, wherein said powercalibration area of said second recording layer has an area notoverlapped on said power calibration area of said first recording layer.5. The optical recording medium according to claim 1, wherein, in saidfirst recording layer or said second recording layer, a direction towardwhich data is recorded in a user data area and a direction toward whicha partition in an optimum power control area is used are different fromeach other.
 6. The optical recording medium according to claim 1,wherein a recommended recording power value for each of said recordinglayers is beforehand recorded.
 7. The optical recording medium accordingto claim 2, wherein a recommended recording power value for each of saidrecording layers is beforehand recorded.
 8. The optical recording mediumaccording to claim 3, wherein a recommended recording power value foreach of said recording layers is beforehand recorded.
 9. The opticalrecording medium according to claim 4, wherein a recommended recordingpower value for each of said recording layers is beforehand recorded.10. The optical recording medium according to claim 5, wherein arecommended recording power value for each of said recording layers isbeforehand recorded.
 11. A recording method for an optical recordingmedium comprising: said optical recording medium including anoptical-transmissible first substrate; a first recording layer disposedon said first substrate, on which information can be recorded byirradiating a laser beam from the first substrate's side; a secondrecording layer disposed on said first recording layer, on whichinformation can be recorded by irradiating said laser beam; and each ofsaid first recording layer and said second recording layer includingpower calibration areas to optimizing intensity of said laser beam;recording of information on said first recording layer and recording ofinformation in said second recording layer are performed forwardopposite directions.
 12. The recording method for the optical recordingmedium according to claim 11, wherein recording of information on saidfirst recording layer is performed before recording of information onsaid second recording layer.
 13. The recording method for the opticalrecording medium according to claim 12, wherein a part of said firstrecording layer overlapping on said power calibration area of saidsecond recording layer is in a previously-recorded state.
 14. Therecording method for the optical recording medium according to claim 11,wherein said power calibration area of said second recording layer hasan area not overlapped on said power calibration area of said firstrecording layer.
 15. The recording method for the optical recordingmedium according to claim 11, wherein, in said first recording layer orsaid second recording layer, a direction toward which data is recordedin a user data area and a direction toward which a partition in anoptimum power control area is used are different from each other.